the membranes of the endoplasmic reticulum are continuous with
Endoplasmic reticulum


The endoplasmic reticulum (ER) is a type of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae. The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum occurs in most types of eukaryotic cells, but is absent from red blood cells and spermatozoa. There are two types of ER: rough endoplasmic reticulum and smooth endoplasmic reticulum. The outer (cytosolic) face of the rough endoplasmic reticulum is studded with ribosomes
9683032
Endoplasmic reticulum


also known to stay associated with translocons. The membrane of the rough endoplasmic reticulum forms large double membrane sheets that are located near, and continuous with, the outer layer of the nuclear envelope. The double membrane sheets are stacked and connected through several right or left-handed helical ramps, the so-called Terasaki ramps, giving rise to a structure resembling a multi-storey car park. Although there is no continuous membrane between the endoplasmic reticulum and the Golgi apparatus, membrane-bound transport vesicles shuttle proteins between these two
9683038
Endoplasmic reticulum


Claude, and Ernest F. Fullam. Later, the word "reticulum", which means "network", was applied by Porter in 1953 to describe this fabric of membranes. The general structure of the endoplasmic reticulum is a network of membranes called cisternae. These sac-like structures are held together by the cytoskeleton. The phospholipid membrane encloses the cisternal space (or lumen), which is continuous with the perinuclear space but separate from the cytosol. The functions of the endoplasmic reticulum can be summarized as the synthesis and export
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Glycan


of the endoplasmic reticulum membrane. Five mannose residues are then added to this structure. At this point, the partially finished core glycan is flipped across the endoplasmic reticulum membrane, so that it is now located within the reticular lumen. Assembly then continues within the endoplasmic reticulum, with the addition of four more mannose residues. Finally, three glucose residues are added to this structure. Following full assembly, the glycan is transferred en bloc by the glycosyltransferase oligosaccharyltransferase to a nascent peptide chain, within the reticular lumen. This core structure
16352424
Endoplasmic reticulum


compartments. Vesicles are surrounded by coating proteins called COPI and COPII. COPII targets vesicles to the Golgi apparatus and COPI marks them to be brought back to the rough endoplasmic reticulum. The rough endoplasmic reticulum works in concert with the Golgi complex to target new proteins to their proper destinations. A second method of transport out of the endoplasmic reticulum involves areas called membrane contact sites, where the membranes of the endoplasmic reticulum and other organelles are held closely together, allowing the transfer of lipids and other small molecules. The rough endoplasmic reticulum
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Inner nuclear membrane protein


the outer nuclear membrane is continuous with the endoplasmic reticulum it is possible that the inner nuclear membrane proteins are translated on the rough endoplasmic reticulum, whereby the proteins move into the nucleus by lateral diffusion through a nuclear pore. In this model, proteins diffuse freely from the ER to the inner nuclear membrane, where association with nuclear lamina or chromatin immobilizes them. A nuclear localisation signal (NLS) is not sufficient to target a protein to the INM, and the N-terminal domain of LBR cannot translocate into the nuclear
21568345
Oxysterol-binding protein


transport between the endoplasmic reticulum and the plasma membrane. Although sterol transfer is proposed to occur at regions where organelle membranes are closely apposed, disruption of endoplasmic reticulum-plasma membrane contact sites do not have major effects on sterol transfer, though phospholipid homeostasis is perturbed. Various ORPs confine at membrane contacts sites (MCS), where endoplasmic reticulum (ER) is apposed with other organelle limiting membranes. Yeast ORPs also participate in vesicular trafficking, in which they affect Sec14-dependent Golgi vesicle biogenesis and, later in post-Golgi exocytosis,
136008
Endoplasmic reticulum


of proteins and membrane lipids, but varies between ER and cell type and cell function. The quantity of both rough and smooth endoplasmic reticulum in a cell can slowly interchange from one type to the other, depending on the changing metabolic activities of the cell. Transformation can include embedding of new proteins in membrane as well as structural changes. Changes in protein content may occur without noticeable structural changes. The surface of the rough endoplasmic reticulum (often abbreviated RER or Rough ER) (also called "granular endoplasmic reticulum") is
9683035
Endoplasmic reticulum membrane protein complex


The endoplasmic reticulum membrane protein complex (EMC) is a putative endoplasmic reticulum-resident membrane protein (co-)chaperone. The EMC is evolutionarily conserved in eukaryotes (animals, plants, and fungi), and its initial appearance might reach back to the last eukaryotic common ancestor (LECA). Many aspects of mEMC biology and molecular function remain to be studied. , the structure of the EMC has not yet been resolved. The EMC consists of up to 10 subunits (EMC1 - EMC4, MMGT1, EMC6 - EMC10), of
10853598
Jean Vance


active enzymes able to synthesize a variety of membrane components. She proposed that the MAM might function as a "membrane bridge" between the endoplasmic reticulum and the mitochondria. Although Vance's work was ahead of its time, it was rediscovered in the late 2000's when other researchers began to identify specific proteins, called tethers, that form the contact points between organelles. The mitochondria-endoplasmic reticulum bridge Vance originally identified is now named the endoplasmic reticulum membrane protein complex and has been shown to be important in the function, positioning
6938847
Endomembrane system


be either transmembrane proteins, which become embedded in the membrane of the endoplasmic reticulum, or water-soluble proteins, which are able to pass through the membrane into the lumen. Those that reach the inside of the endoplasmic reticulum are folded into the correct three-dimensional conformation. Chemicals, such as carbohydrates or sugars, are added, then the endoplasmic reticulum either transports the completed proteins, called secretory proteins, to areas of the cell where they are needed, or they are sent to the Golgi apparatus for further processing and
9903449
Ribophorin


Ribophorins are transmembrane glycoproteins which are located in the membrane of the rough endoplasmic reticulum, but are absent in the membrane of the smooth endoplasmic reticulum. There are two types of ribophorines: ribophorin I and II. These act in the proteic complex oligosaccharyltransferase (OST) as two different subunits of the named complex. Ribophorin I and II are only present in eukaryote cells. Both types of ribophorins develop a key role in the binding of ribosomes to the rough endoplasmic reticulum as well as in the co-translational processes that depend on
5396534
Gene expression


cytoplasmic proteins and the membrane of the endoplasmic reticulum for proteins that are for export from the cell or insertion into a cell membrane. Proteins that are supposed to be expressed at the endoplasmic reticulum are recognised part-way through the translation process. This is governed by the signal recognition particle—a protein that binds to the ribosome and directs it to the endoplasmic reticulum when it finds a signal peptide on the growing (nascent) amino acid chain. Each protein exists as an unfolded polypeptide or random coil when translated from a sequence
791894
Derlin-1


Derlin-1 also known as degradation in endoplasmic reticulum protein 1 is a membrane protein that in humans is encoded by the "DERL1" gene. Derlin-1 is located in the membrane of the endoplasmic reticulum (ER) and is involved in retrotranslocation of specific misfolded proteins and in ER stress. Derlin-1 is widely expressed in thyroid, fat, bone marrow and many other tissues. The protein belongs to the Derlin-family proteins (also called derlins) consisting of derlin-1, derlin-2 and derlin-3 that are components in the endoplasmic reticulum-associated protein
560017
Endoplasmic reticulum


that are the sites of protein synthesis. The rough endoplasmic reticulum is especially prominent in cells such as hepatocytes. The smooth endoplasmic reticulum lacks ribosomes and functions in lipid synthesis but not metabolism, the production of steroid hormones, and detoxification. The smooth ER is especially abundant in mammalian liver and gonad cells. The ER was observed with light microscope by Garnier in 1897, who coined the term "ergastoplasm". With electron microscopy, the lacy membranes of the endoplasmic reticulum were first seen in 1945 by Keith R. Porter, Albert
9683033
Hepacivirus C


membrane protein with 4 transmembrane domains. It is located within the endoplasmic reticulum and plays an important role for recruitment of other viral proteins. It induces morphological changes to the endoplasmic reticulum forming a structure termed the membranous web. NS5A is a hydrophilic phosphoprotein which plays an important role in viral replication, modulation of cell signaling pathways and the interferon response. It is known to bind to endoplasmic reticulum anchored human VAP proteins. The NS5B protein (65 kDa) is the viral RNA dependent RNA polymerase. NS5B has the key function of
5976147
Endoplasmic reticulum


and the products of these enzymes. The sarcoplasmic reticulum (SR), from the Greek σάρξ "sarx" ("flesh"), is smooth ER found in myocytes. The only structural difference between this organelle and the smooth endoplasmic reticulum is the medley of proteins they have, both bound to their membranes and drifting within the confines of their lumens. This fundamental difference is indicative of their functions: The endoplasmic reticulum synthesizes molecules, while the sarcoplasmic reticulum stores calcium ions and pumps them out into the sarcoplasm when the muscle
9683043
C-5 sterol desaturase


desaturase appears to have four to five membrane-spanning regions, suggesting that it is a transmembrane protein. C5SD activity has been demonstrated in microsomes from rat tissue, implying that rat enzyme localizes to the endoplasmic reticulum Fluorescence microscopy experiments have shown that in the ciliate "Tetrahymena thermophila" C5SD localizes to the endoplasmic reticulum and that in "S. cerevisiae" C5SD localizes to both the endoplasmic reticulum and vesicles. In "Arabidopsis thaliana" C5SD is located in both the endoplasmic reticulum and lipid particles. The common class of antifungal drugs known
8720729
Endomembrane system


the membrane's life. One unifying characteristic the membranes share is a lipid bilayer, with proteins attached to either side or traversing them. Most lipids are synthesized in yeast either in the endoplasmic reticulum, lipid particles, or the mitochondrion, with little or no lipid synthesis occurring in the plasma membrane or nuclear membrane. Sphingolipid biosynthesis begins in the endoplasmic reticulum, but is completed in the Golgi apparatus. The situation is similar in mammals, with the exception of the first few steps in ether lipid biosynthesis, which occur in peroxisomes
9903433
Yop1p


DP1/Yop1p is an integral membrane protein family that, along with the reticulons, is responsible for the shape of the tubular endoplasmic reticulum (ER) in yeast and mammalian cells. Furthermore, it is also believed that they might be involved in sheet ER formation. About half the total area of membrane in an eukaryotic cell encloses the space of the endoplasmic reticulum. The ER is an extremely dynamic membrane organelle which consists of the nuclear envelope and the peripheral ER. It is organized into a netlike labyrinth of branching tubules and
3218332
FFAT motif


targeted to the endoplasmic reticulum, with the exception of OSBP, and PITPNM1 (the fly homologue of which is called RdgB). Instead, they were known for their localization to other sites especially the "trans" Golgi network (OSBP, Osh1p and CERT) and the plasma membrane (Osh2p, Osh3p). The discovery that these proteins also targeted the endoplasmic reticulum led to a far more detailed analysis of their targeting, and revealed that all the FFAT-containing lipid transfer proteins are present at both the endoplasmic reticulum and
14126429
Phosphatidylethanolamine


lecithin and is produced commercially using chromatographic separation. Synthesis of Phosphatidylethanolamine through the phosphatidylserine decarboxylation pathway occurs rapidly in the inner mitochondrial membrane. However, phosphatidylserine is made in the endoplasmic reticulum. Because of this, the transport of phosphatidylserine from the endoplasmic reticulum to the mitochondrial membrane and then to the inner mitochondrial membrane limits the rate of synthesis via this pathway. The mechanism for this transport is currently unknown, but may play a role in regulation of the rate of synthesis in this pathway. Phosphatidylethanolamines in food break down to form phosphatidylethanolamine
17460816
JPH1


Junctophilin-1 is a protein that in humans is encoded by the "JPH1" gene. Junctional complexes between the plasma membrane and endoplasmic/sarcoplasmic reticulum are a common feature of all excitable cell types and mediate cross talk between cell surface and intracellular ion channels. The protein encoded by this gene is a component of junctional complexes and is composed of a C-terminal hydrophobic segment spanning the endoplasmic/sarcoplasmic reticulum membrane and a remaining cytoplasmic domain that shows specific affinity for the plasma membrane. This gene is a member of the junctophilin gene
19286717
Oligosaccharyltransferase


pathway. OST is a component of the translocon in the endoplasmic reticulum (ER) membrane. A lipid-linked core-oligosaccharide is assembled at the membrane of the endoplasmic reticulum and transferred to selected asparagine residues of nascent polypeptide chains by the oligosaccharyl transferase complex. The active site of OST is located about 4 nm from the lumenal face of the ER membrane. It usually acts during translation as the nascent protein is entering the ER, but this cotranslational glycosylation is nevertheless called a posttranslational modification. A few examples have been found
4359934
STIM1


Stromal interaction molecule 1 is a protein that in humans is encoded by the "STIM1" gene. STIM1 has a single transmembrane domain, and is localized to the endoplasmic reticulum, and to a lesser extent to the plasma membrane. Even though the protein has been identified earlier, its function was unknown until recently. In 2005, it was discovered that STIM1 functions as a calcium sensor in the endoplasmic reticulum. Upon activation of the IP3 receptor, the calcium concentration in the endoplasmic reticulum decreases, which is sensed by STIM1,
2703511
Endoplasmic reticulum


the translocon, a membrane-embedded multiprotein complex. Proteins that are destined for places outside the endoplasmic reticulum are packed into transport vesicles and moved along the cytoskeleton toward their destination. In human fibroblasts, the ER is always co-distributed with microtubules and the depolymerisation of the latter cause its co-aggregation with mitochondria, which are also associated with the ER. The endoplasmic reticulum is also part of a protein sorting pathway. It is, in essence, the transportation system of the eukaryotic cell. The majority of its resident
9683047
Endoplasmic reticulum


ER has many functions. It synthesizes lipids, phospholipids, and steroids. Cells which secrete these products, such as those in the testes, ovaries, and sebaceous glands have an abundance of smooth endoplasmic reticulum. It also carries out the metabolism of carbohydrates, detoxification of natural metabolism products and of alcohol and drugs, attachment of receptors on cell membrane proteins, and steroid metabolism. In muscle cells, it regulates calcium ion concentration. Smooth endoplasmic reticulum is found in a variety of cell types (both animal and plant),
9683041
Endoplasmic reticulum


as a potential cause of damage in hypoxia/ischemia, insulin resistance, and other disorders. Secretory proteins, mostly glycoproteins, are moved across the endoplasmic reticulum membrane. Proteins that are transported by the endoplasmic reticulum throughout the cell are marked with an address tag called a signal sequence. The N-terminus (one end) of a polypeptide chain (i.e., a protein) contains a few amino acids that work as an address tag, which are removed when the polypeptide reaches its destination. Nascent peptides reach the ER via
9683046
Bare lymphocyte syndrome


TAP2, TAP1, or TAPBP deficiencies. The TAP proteins are involved in pumping degraded cytosolic peptides across the endoplasmic reticulum membrane so they can bind HLA class I. Once the peptide:HLA class I complex forms, it is transported to the membrane of the cell. However, a defect in the TAP proteins prevents pumping of peptides into the endoplasmic reticulum so no peptide:HLA class I complexes form, and therefore, no HLA class I is expressed on the membrane. Just like BLS II, the defect isn't in the
21389940
LiMETER


LiMETER stands for light-inducible membrane-tethered peripheral endoplasmic reticulum (ER). LiMETER is an optogenetics tool designed to reversibly label cortical ER or the apposition between plasma membrane (PM) and endoplasmic reticulum (ER) membranes (termed as ER-PM junctions). The ER luminal domain of LiMETER contains a signal peptide and the transmembrane domain derived from STIM1, with GFP placed in between as a reporter. STIM1 is an ER-resident calcium sensor protein responsible for sensing calcium changes in internal calcium stores and communicate with
21592763
JPH3


Junctophilin-3 is a protein that in humans is encoded by the "JPH3" gene. Junctional complexes between the plasma membrane and endoplasmic/sarcoplasmic reticulum are a common feature of all excitable cell types and mediate cross talk between cell surface and intracellular ion channels. The protein encoded by this gene is a component of junctional complexes and is composed of a C-terminal hydrophobic segment spanning the endoplasmic/sarcoplasmic reticulum membrane and a remaining cytoplasmic domain that shows specific affinity for the plasma membrane. CAG/CTG repeat expansions at the Huntington's
6470619
Disc shedding


rod, these discs lack any direct connection to the surface membrane (with the exception of a few recently formed basal discs that remain in continuity with the surface), the cone’s photosensitive membrane is continuous with the surface membrane. The outer segment (OS) discs are densely packed with rhodopsin for high-sensitivity light detection. These discs are completely replaced once every ten days and this continuous renewal continues throughout the lifetime of the sighted animal. Opsin is synthesized on the rough endoplasmic reticulum and is an integral membrane protein.
5097352
Nuclear envelope


. The outer nuclear membrane also shares a common border with the endoplasmic reticulum. While it is physically linked, the outer nuclear membrane contains proteins found in far higher concentrations than the endoplasmic reticulum. All four nesprin proteins (nuclear envelope spectrin repeat proteins) present in mammals are expressed in the outer nuclear membrane. Nesprin proteins connect cytoskeletal filaments to the nucleoskeleton. Nesprin-mediated connections to the cytoskeleton contribute to nuclear positioning and to the cell’s mechanosensory function. KASH domain proteins of Nesprin-1 and -2 are part of a LINC complex
21175984
Cell nucleus


cellular membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 nanometres (nm). The nuclear envelope completely encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm and the cytoplasm. The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (RER), and is similarly studded with ribosomes. The space between the membranes is called the perinuclear space and is continuous
6416538
Translation (biology)


. The tRNAs carry specific amino acids that are chained together into a polypeptide as the mRNA passes through and is read by the ribosome. Translation proceeds in three phases: In prokaryotes (bacteria), translation occurs in the cytosol, where the medium and small subunits of the ribosome bind to the tRNA. In eukaryotes, translation occurs in the cytosol or across the membrane of the endoplasmic reticulum in a process called transposition. In transposition, the entire ribosome/mRNA complex binds to the outer membrane of the rough endoplasmic reticulum (
18110987
Endomembrane system


from the cytoplasm. It has two membranes, each a lipid bilayer with associated proteins. The outer nuclear membrane is continuous with the rough endoplasmic reticulum membrane, and like that structure, features ribosomes attached to the surface. The outer membrane is also continuous with the inner nuclear membrane since the two layers are fused together at numerous tiny holes called nuclear pores that perforate the nuclear envelope. These pores are about 120 nm in diameter and regulate the passage of molecules between the nucleus and cytoplasm, permitting some to pass through the membrane
9903436
Raymond J. Deshaies


secretory and membrane proteins into the endoplasmic reticulum of all eukaryotic cells. He went on to identify a complex of proteins that form the translocon in yeast cells. In addition, Deshaies discovered a role for 70 kilodalton heat shock proteins (Hsp70s) in enabling the post-translational insertion of proteins into the endoplasmic reticulum and mitochondrial membranes. This was the first specific, genetically- and biochemically-validated function to be discovered for a member of the Hsp70 family of proteins. SCF and cullin–RING ubiquitin ligases: As a postdoctoral fellow
12728633
Signal recognition particle RNA


endoplasmic reticulum (ER). In Archaea, SRP delivers proteins to the plasma membrane. In the bacteria, SRP primarily incorporates proteins into the inner membrane. SRP participates also in the sorting of proteins after their synthesis has been completed (post-translational protein sorting). In eukaryotes, tail-anchored proteins possessing a hydrophobic insertion sequence at their C-terminus are delivered to the endoplasmic reticulum (ER) by the SRP. Similarly, the SRP assists post-translationally in the import of nuclear-encoded proteins to the
6338489
Ceramide phosphoethanolamine synthase


, specifically those transferring non-standard substituted phosphate groups. In mammalian cells, two CPE synthase activities have been described, one resides in the endoplasmic reticulum, and the other one is associated with the plasma membrane. The endoplasmic reticulum-resident CPE synthase, SMSr, is identified as a monofunctional CPE synthase produces trace amounts of CPE. On the other hand, mammalian CPE synthase that is on the plasma membrane, SMS2, is a bifunctional enzyme that produces both CPE and sphingomyelin, thus also functioning as a sphingomyelin synthase.
13097355
FFAT motif


: VAPA, VAPB and MOSPD2. All of these share a conserved major sperm protein domain in the cytoplasm anchored to the endoplasmic reticulum membrane by a largely unstructured linker leading to a transmembrane domain. MOSPD2 additionally at its amino-terminus has a lipid transfer domain in the CRAL/TRIO domain family. The main yeast homolog is Scs2p, which has the same domain architecture as VAPA and VAPB, and is also an integral membrane protein of the endoplasmic reticulum. Many of the proteins with FFAT motifs were previously not known to be
14126428
MMP27


which is not secreted and is efficiently retained in the endoplasmic reticulum in three mammalian cell lines. Deletion mutants and swapping with recombinant MMP-10 demonstrate that the unique MMP-27 C-terminal extension (CTE) is necessary and sufficient for endoplasmic reticulum retention but does not provide a stable membrane anchorage. Despite sequence homology with MT-MMPs, the CTE is not a transmembrane domain and does not interact permanently with membrane. This unique feature for an MMP raises important questions about potential functions of MMP-27, which remains to be investigated. Sparse information
18644079
GOLM1


Golgi membrane protein 1 (GOLM1) also known as Golgi phosphoprotein 2 or Golgi membrane protein GP73 is a protein that in humans is encoded by the "GOLM1" gene. Two alternatively spliced transcript variants encoding the same protein have been described for this gene. The Golgi complex plays a key role in the sorting and modification of proteins exported from the endoplasmic reticulum. The protein encoded by this gene is a type II Golgi transmembrane protein. It processes protein synthesized in the rough endoplasmic reticulum and assists in the transport of protein cargo
1874125
Endoplasmic-reticulum-associated protein degradation


on the ER membrane and targets newly-made CD4 in the endoplasmic reticulum for degradation by cytosolic proteasomes. Vpu only utilizes part of the ERAD process to degrade CD4. CD4 is normally a stable protein and is not likely to be a target for ERAD. However, HIV produces the membrane protein Vpu that binds to CD4.The Vpu protein mainly retains the CD4 in the ER by SCFβ-TrCP-dependent ubiquitination of the CD4 cytosolic tail and transmembrane domain (TMD) interactions. The CD4 Gly415 is a contributor to CD4-Vpu interactions,
18988016
Nuclear envelope


complexes break apart simultaneously. Biochemical evidence suggests that the nuclear pore complexes disassemble into stable pieces rather than disintegrating into small polypeptide fragments. M-Cdk's also phosphorylate elements of the nuclear lamina (the framework that supports the envelope) leading to the disassembly of the lamina and hence the envelope membranes into small vesicles. Electron and fluorescence microscopy has given strong evidence that the nuclear membrane is absorbed by the endoplasmic reticulum—nuclear proteins not normally found in the endoplasmic reticulum show up during mitosis. In addition to the breakdown of the
21175989
Sodium phenylbutyrate


protein, ΔF508-CFTR, causes it to be unstable and misfold, hence trapped in the endoplasmic reticulum and unable to reach the cell membrane. This lack of CFTR in the cell membrane leads to disrupted chloride transport and the symptoms of cystic fibrosis. Sodium phenylbutyrate can act as a chemical chaperone, stabilising the mutant CFTR in the endoplasmic reticulum and allowing it to reach the cell surface. Deriving from its activity as a histone deacetylase inhibitor, sodium phenylbutyrate is under investigation for use as a potential differentiation-inducing agent in malignant glioma and
21292453
Milk fat globule membrane


are secreted in a unique manner by lactocytes, which are specialized epithelial cells within the alveoli of the lactating mammary gland. The process takes place in multiple stages. First, fat synthesized within the endoplasmic reticulum accumulates in droplets between the inner and outer phospholipid monolayers of the endoplasmic reticulum membrane. As these droplets increase in size, the two monolayers separate further and eventually pinch off. This leads to the surrounding of the droplet in a phospholipid monolayer that allows it to disperse within the aqueous cytoplasm. In the next stage, lipid
21508798
Calcium signaling


the cytosol to the extracellular space, the endoplasmic reticulum (ER), and sometimes into the mitochondria. Certain proteins of the cytoplasm and organelles act as buffers by binding Ca. Signaling occurs when the cell is stimulated to release Ca ions from intracellular stores, and/or when Ca enters the cell through plasma membrane ion channels. Specific signals can trigger a sudden increase in the cytoplasmic Ca level up to 500–1,000 nM by opening channels in the endoplasmic reticulum or the plasma membrane. The most common signaling pathway that increases cytoplasmic calcium concentration is
18719569
Hepacivirus C


. The endoplasmic reticulum in particular are deformed into uniquely shaped membrane structures termed 'membranous webs'. These structures can be induced by sole expression of the viral protein NS4B. The core protein associates with lipid droplets and utilises microtubules and dyneins to alter their location to a perinuclear distribution. Release from the hepatocyte may involve the very low density lipoprotein secretory pathway. Another hypothesis states that the viral particle may be secreted from the endoplasmic reticulum through the endosomal-sorting complex required for transport (ESCRT) pathway. This pathway is normally utilized
5976156
Bovine foamy virus


begin to bud. Most bud into the endoplasmic reticulum which are then packaged and distributed to other cells. Some particles manage to escape through the membrane but this number is usually quite low. Being a spumavirus, bovine foamy virus has a unique life cycle, even when compared to other retroviruses. One of these differences is the mechanism used in the budding process. Rather than budding through the plasma membrane like a more traditional retrovirus, BFV and other foamy viruses bud using the endoplasmic reticulum. Another facet of BFV that makes it
6509075
Nuclear envelope


The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes which in eukaryotic cells surrounds the nucleus, which encases the genetic material. The nuclear envelope consists of two lipid bilayer membranes, an inner nuclear membrane, and an outer nuclear membrane. The space between the membranes is called the perinuclear space. It is usually about 20–40 nm wide. The outer nuclear membrane is continuous with the endoplasmic reticulum membrane. The nuclear envelope has many nuclear pores that allow materials to move between the cytosol
21175982
David D. Sabatini


a postdoctoral fellow at Rockefeller, Sabatini entered the Rockefeller graduate program from which he received a PhD in 1966 for studies on protein translation by ribosomes attached to endoplasmic reticulum membranes. Sabatini's research has focused on the mechanisms by which proteins are targeted to different organelles within the cell. His early work studied co-translational targeting of ribosomes to the endoplasmic reticulum and helped establish the hypothesis that signal peptides direct protein traffic to cellular compartments. He later focused on trafficking from the Golgi apparatus to secretory vesicles and to the plasma membrane and
734754
Biological membrane


types of membranes differ in lipid and protein composition. Distinct types of membranes also create intracellular organelles: endosome; smooth and rough endoplasmic reticulum; sarcoplasmic reticulum; Golgi apparatus; lysosome; mitochondrion (inner and outer membranes); nucleus (inner and outer membranes); peroxisome; vacuole; cytoplasmic granules; cell vesicles (phagosome, autophagosome, clathrin-coated vesicles, COPI-coated and COPII-coated vesicles) and secretory vesicles (including synaptosome, acrosomes, melanosomes, and chromaffin granules). Different types of biological membranes
4613378
Thylakoid


fluidity linolenic acid are synthesized in a complex pathway involving exchange of lipid precursors between the endoplasmic reticulum and inner membrane of the plastid envelope and transported from the inner membrane to the thylakoids via vesicles. The thylakoid lumen is a continuous aqueous phase enclosed by the thylakoid membrane. It plays an important role for photophosphorylation during photosynthesis. During the light-dependent reaction, protons are pumped across the thylakoid membrane into the lumen making it acidic down to pH 4. In higher plants thylakoids are organized into a granum-stroma membrane assembly.
753102
Phosphodiesterase 3


similar pharmacological and kinetic properties, but the distinction is in expression profiles and affinity for cGMP. PDE3A is mainly implicated in cardiovascular function and fertility but PDE3B is mainly implicated in lipolysis. Table 1 is an overview of localization of the PDE3 isoforms. In general, PDE3 can be either cytosolic or membrane-bound and has been associated to plasma membrane, sarcoplasmic reticulum, golgi, and nucleus envelope. PDE3B is predominantly membrane-associated, and is localized to endoplasmic reticulum and microsomal fractions. PDE3A can be either membrane-associated
15404171
Telophase


are dismantled during prophase and prometaphase and reconstructed during telophase, when the nuclear envelope reforms on the surface of separated sister chromatids. The nuclear membrane is fragmented and partly absorbed by the endoplasmic reticulum during prometaphase and the targeting of inner nuclear membrane protein-containing ER vesicles to the chromatin occurs during telophase in a reversal of this process. Membrane-forming vesicles aggregate directly to the surface of chromatin, where they fuse laterally into a continuous membrane. Ran-GTP is required for early nuclear envelope assembly at the surface of the chromosomes
4020026
ORAI1


the depletion of internal calcium stores, which is called the "store-operated" or the "capacitative" mechanism. They are molecular constituents of the "calcium release activated calcium currents" (ICRAC). Upon activation of phospholipase C by various cell surface receptors, inositol trisphosphate is formed that releases calcium from the endoplasmic reticulum. The decreased calcium concentration in the endoplasmic reticulum is sensed by the STIM1 protein. STIM1 clusters upon the depletion of the calcium stores and forms "puncta", and relocates near the plasma membrane,
3865125
Heterokont


a retrograde current, pulling the cell through the water or bringing in food. The mastigonemes have a peculiar tripartite structure, which may be taken as the defining characteristic of the heterokonts, thereby including a few protists that do not produce cells with the typical heterokont form. Mastigonemes have been lost in a few heterkont lines, most notably the diatoms. Many heterokonts are algae with chloroplasts surrounded by four membranes, which are counted from the outermost to the innermost membrane. The first membrane is continuous with the host's chloroplast endoplasmic reticulum
18256403
Endomembrane system


the nuclear envelope. More than half the total membrane in eukaryotic cells is accounted for by the ER. The ER is made up of flattened sacs and branching tubules that are thought to interconnect, so that the ER membrane forms a continuous sheet enclosing a single internal space. This highly convoluted space is called the ER lumen and is also referred to as the ER cisternal space. The lumen takes up about ten percent of the entire cell volume. The endoplasmic reticulum membrane allows molecules to be selectively transferred between the lumen and the
9903440
Golgi apparatus


thus creating proteoglycans. Glycosaminoglycans are long unbranched polysaccharide molecules present in the extracellular matrix of animals. The vesicles that leave the rough endoplasmic reticulum are transported to the "cis" face of the Golgi apparatus, where they fuse with the Golgi membrane and empty their contents into the lumen. Once inside the lumen, the molecules are modified, then sorted for transport to their next destinations. Those proteins destined for areas of the cell other than either the endoplasmic reticulum or the Golgi apparatus are moved through the Golgi cisternae towards the "
12380550
Vpu protein


Vpu is an accessory protein that in HIV is encoded by the "vpu" gene. Vpu stands for "Viral Protein U". The Vpu protein acts in the degradation of CD4 in the endoplasmic reticulum and in the enhancement of virion release from the plasma membrane of infected cells. Vpu induces the degradation of the CD4 viral receptor and therefore participates in the general downregulation of CD4 expression during the course of HIV infection. Vpu-mediated CD4 degradation is thought to prevent CD4-Env binding in the endoplasmic reticulum in order to facilitate proper
16689438
Bestrophin 1


gene is essential for protein functioning and mislocalization is often connected to a variety of retinal degenerative diseases. The BEST1 gene expresses the Best1 protein primarily in the cytosol of the retinal pigment epithelium. The protein is typically contained in vesicles near the cellular membrane. There is also research to support that the Best1 protein is localized and produced in the endoplasmic reticulum (intracellular organelle involved in protein and lipid synthesis). Best1 is typically expressed with other proteins also synthesized in the endoplasmic reticulum, such as calreticulin, calnexin and Stim-1. Calcium
20446187
EIF2AK3


Eukaryotic translation initiation factor 2-alpha kinase 3, also known as protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), is an enzyme that in humans is encoded by the "EIF2AK3" gene. The protein encoded by this gene phosphorylates the alpha subunit of eukaryotic translation-initiation factor 2 (EIF2), leading to its inactivation, and thus to a rapid reduction of translational initiation and repression of global protein synthesis. It is a type I membrane protein located in the endoplasmic reticulum (ER), where it is induced
20847741
N-linked glycosylation


the ER membrane. This reaction is driven by the energy released from the cleavage of the pyrophosphate bond between the dolichol-glycan molecule. There are three conditions to fulfill before a glycan is transferred to a nascent polypeptide: Oligosaccharyltransferase is the enzyme responsible for the recognition of the consensus sequence and the transfer of the precursor glycan to a polypeptide acceptor which is being translated in the endoplasmic reticulum lumen. N-linked glycosylation is therefore, is a co-translational event N-glycan processing is carried out in endoplasmic reticulum and the
21189501
Endoplasmic reticulum


studded with protein-manufacturing ribosomes giving it a "rough" appearance (hence its name). The binding site of the ribosome on the rough endoplasmic reticulum is the translocon. However, the ribosomes are not a stable part of this organelle's structure as they are constantly being bound and released from the membrane. A ribosome only binds to the RER once a specific protein-nucleic acid complex forms in the cytosol. This special complex forms when a free ribosome begins translating the mRNA of a protein destined for the secretory pathway
9683036
Lipid bilayer


bilayers, while other sub-cellular structures are surrounded by a single lipid bilayer (such as the plasma membrane, endoplasmic reticula, Golgi apparatus and lysosomes). See Organelle. Prokaryotes have only one lipid bilayer- the cell membrane (also known as the plasma membrane). Many prokaryotes also have a cell wall, but the cell wall is composed of proteins or long chain carbohydrates, not lipids. In contrast, eukaryotes have a range of organelles including the nucleus, mitochondria, lysosomes and endoplasmic reticulum. All of these sub
331724
Fluorescence loss in photobleaching


of FLIP is to determine the continuity of membranous organelles. This continuity or lack thereof is determined by observing the amount of fluorescence in the region of interest. If there is a complete loss of fluorescence, this indicates that the organelles are continuous. However, if there is incomplete loss of fluorescence, then there is not continuity between the organelles. Instead, these organelles are compartmentalized and therefore closed off to the transfer of any photobleached fluorophores. Continuity of the Golgi apparatus, endoplasmic reticulum, and nucleus have been verified using FLIP
1497107
JPH2


Junctophilin 2, also known as JPH2, is a protein which in humans is encoded by the "JPH2" gene. Alternative splicing has been observed at this locus and two variants encoding distinct isoforms are described. Junctional complexes between the plasma membrane and endoplasmic/sarcoplasmic reticulum are a common feature of all excitable cell types and mediate cross talk between cell surface and intracellular ion channels. The protein encoded by this gene is a component of junctional complexes and is composed of a C-terminal hydrophobic segment spanning the endoplasmic/sarcoplasmic reticulum
10079916
Glucose-6-phosphate translocase


highly involved in the regulation of homeostasis and blood glucose levels. Within this framework of glucose regulation, the translocase components are responsible for transporting the substrates and products across the endoplasmic reticulum membrane, resulting in the release of free glucose into the bloodstream. Glucose-6-Phosphate Translocase is a transmembrane protein providing a selective channel between the endoplasmic reticulum lumen and the cytosol. The enzyme is made up of three separate transporting subunits referred to as G6PT1 (subunit 1), G6PT2 (subunit 2) and G6PT3 (subunit 3). While the hydrolyzing
10276363
Endoplasmic reticulum membrane protein complex


which only two (EMC8/9) are homologous proteins. Seven out of ten (EMC1, EMC3, EMC4, MMMGT1, EMC6, EMC7, EMC10) subunts are predicted to contain at least one transmembrane domain (TMD), whereas EMC2, EMC8 and EMC9 do not contain any predicted transmembrane domains are herefore likely to interact with the rest of the EMC on the cytosolic face of the endoplasmic reticulum (ER). EMC proteins are thought to be present in the mature complex in a 1:1 stoichiometry. The majority of EMC proteins
10853599
Opipramol


proteins located in the endoplasmic reticulum. σ receptors play key role in potentiating intracellular calcium mobilization thereby acting as sensor or modulator of calcium signaling. Occupancy of σ receptors by agonists causes translocation of the receptor from endoplasmic reticulum to peripheral areas (membranes) where the σ receptors cause neurotransmitter release. Opipramol is said to have a biphasic action, with prompt initial improvement of tension, anxiety, and insomnia followed by improved mood later. Hence, it is an anxiolytic with an antidepressant component. After sub-chronic treatment with opipramol,
12695363
Antigen processing


degradation. Proteasomes break the protein up into peptides that include some around nine amino acids long (suitable for fitting within the peptide binding cleft of MHC class I molecules). Transporter associated with antigen processing (TAP), a protein that spans the membrane of the rough endoplasmic reticulum, transports the peptides into the lumen of the rough endoplasmic reticulum (ER). Also within the rough ER, a series of chaperone proteins, including calnexin, calreticulin, ERp57, and Binding immunoglobulin protein (BiP) facilitates the proper folding of
12832115
Ceramide


from the lysosome at the surface of the endoplasmic reticulum or in endoplasmic reticulum-associated membranes. It should also be noted that the salvage pathway has been estimated to contribute from 50% to 90% of sphingolipid biosynthesis. As a bioactive lipid, ceramide has been implicated in a variety of physiological functions including apoptosis, cell growth arrest, differentiation, cell senescence, cell migration and adhesion. Roles for ceramide and its downstream metabolites have also been suggested in a number of pathological states including cancer, neurodegeneration, diabetes, microbial pathogenesis
16461268
Peter K. Hepler


apparatus and in the phragmoplast and suggested that these membranes may function in controlling the concentration of free calcium in the mitotic apparatus. Along with Susan Wick and Steve Wolniak, Hepler showed that the endoplasmic reticulum contained stores of calcium and suggested that the endoplasmic reticulum may locally control the calcium concentration and thus the polymerization/depolymerization of microtubules. Subsequently, Hepler, along with Dale Callaham, Dahong Zhang, and Patricia Wadsworth, observed calcium ion transients during mitosis and showed that the microinjection of calcium ions into the mitotic spindle does regulate the
17099995
Satellite glial cell


their flattened shape, satellite glial cells contain all common organelles necessary to make cellular products and to maintain the homeostatic environment of the cell. The plasma membrane of SGCs is thin and not very dense, and it is associated with adhesion molecules, receptors for neurotransmitters and other molecules, and ion channels, specifically potassium ion channels. Within individual SGCs, there is both rough endoplasmic reticulum and smooth endoplasmic reticulum, but the latter is much less abundant. Most often the Golgi apparatus and the centrioles in an SGC are found in a
1883766
Calcium release activated channel


Calcium release-activated channels (CRAC) are specialized plasma membrane Ca ion channels. When calcium ions (Ca) are depleted from the endoplasmic reticulum (a major store of Ca) of mammalian cells, the CRAC channel is activated to slowly replenish the level of calcium in the endoplasmic reticulum. The Ca Release-activated Ca (CRAC) Channel (CRAC-C) Family (TC# 1.A.52) is a member of the Cation Diffusion Facilitator (CDF) Superfamily. These proteins typically have between 4 and 6 transmembrane α
1963634
Calcium release activated channel


intracellular stores (components of the endoplasmic reticulum), allowing calcium to be released into the cytosol. In most of the cell, the fall in Ca concentration within the lumen of the Ca-storing organelles subsequently activates plasma membrane Ca channels. STIM1 is a Ca-sensor protein specialized for electrical signaling in the endoplasmic reticulum (ER). It interacts with and mediates store-dependent regulation of both Orai1 and TRPC1 channels. TRPC1+STIM1-dependent SOC requires functional Orai1. STIM1 is the mechanistic 'missing link' between the ER and the
1963640
Tapasin


single TAP molecule. Tapasin contains a C-terminal double-lysine motif (KKKAE) known to maintain membrane proteins in the endoplasmic reticulum. In humans, the tapasin gene lies within the major histocompatibility complex on chromosome 6. Alternative splicing results in three transcript variants encoding different isoforms. Tapasin is a MHC class I antigen-processing molecule present in the lumen of the endoplasmic reticulum. It plays an important role in the maturation of MHC class I molecules in the ER lumen. Tapasin is one component of the peptide-loading
21096805
Signal transduction


plasma membrane to the cytoplasm, thus carrying out intracellular signal transduction. The release of calcium ions from the endoplasmic reticulum into the cytosol results in its binding to signaling proteins that are then activated; it is then sequestered in the smooth endoplasmic reticulum and the mitochondria. Two combined receptor/ion channel proteins control the transport of calcium: the InsP-receptor that transports calcium upon interaction with inositol triphosphate on its cytosolic side; and the ryanodine receptor named after the alkaloid ryanodine, similar to the InsP receptor but having a feedback mechanism
9259699
David D. Sabatini


in particular the mechanisms that address membrane proteins to the different surface domains of epithelial cells for which he employed viral infected epithelial monolayers. After finishing his PhD, Sabatini joined the faculty at Rockefeller and in his own laboratory continued studies on protein trafficking in the ER. With a group of young associates (Nica Borgese, Mark Adelman, and Gert Kreibich), collaborating with Gunter Blobel, he continued research on the mechanism that ensures the co-translational translocation and vectorial discharge of nascent polypeptides into and across the endoplasmic reticulum membrane.
734755
Spine apparatus


. More specifically, the protein translocation site marker (Sec61α) and the Golgi cisternae markers (giantin and α-mannosidase II) have been observed in the spine apparatus. Synaptic activity triggers Ca influx into dendritic spines via NMDA receptors and voltage-dependent calcium channels. Free Ca ions are rapidly removed from the cytoplasm through Na+/Ca2+ exchangers in the plasma membrane and by sarco/endoplasmic reticulum Ca ATPases (SERCA pumps) that mediate Ca uptake into the smooth endoplasmic reticulum (sER). The spine apparatus, as a sub
1194695
Porcine reproductive and respiratory syndrome virus 2


Most of the nonstructural protein (NSPs) assemble and create a complex called the replication and transcription complex (RTC). The complexes then accumulate in the endoplasmic reticulum double membrane vesicles. These complexes direct both replication and transcription. Besides these hints, the exact way in which type 2 PRRSV translates remains a mystery. At the end of replication, the nucleocapsid proteins surround the newly made genome. The new nucleocapsid complex buds from the smooth endoplasmic reticulum and the golgi complex. Through this process the new capsid obtains the required six
14066306
STARD4


StAR-related lipid transfer protein 4 (STARD4) is a soluble protein involved in cholesterol transport. It can transfer up to 7 sterol molecules per minute between artificial membranes. STARD4 may regulate cholesterol levels in many cells, including in the liver. STARD4 has specifically been linked to the movement of cholesterol to the endoplasmic reticulum. The protein is associated with the endoplasmic reticulum and lipid droplets. Increases in the protein relate to cell stress. High levels of STARD4 increases the synthesis of bile acids and cholesterol esters in liver hepatocytes.
15677991
Stimulator of interferon genes


, ovary, heart, smooth muscle, retina, bone marrow and vagina. The subcellular localization of STING has been elucidated as an endoplasmic reticulum protein. Also, it is likely that STING associates in close proximity with mitochondria associated ER membrane (MAM)-the interface between the mitochondrion and the ER. During intracellular infection, STING is able to relocalize from endoplasmic reticulum to perinuclear vesicles potentially involved in exocyst mediated transport. STING has also been shown to colocalize with autophagy proteins, microtubule-associated protein 1 light chain 3 (LC3) and
20437101
Hepacivirus C


envelope protein. Both envelope proteins (E1 and E2) are highly glycosylated and important in cell entry. E1 serves as the fusogenic subunit and E2 acts as the receptor binding protein. E1 has 4–5 N-linked glycans and E2 has 11 N-glycosylation sites. The p7 protein is dispensable for viral genome replication but plays a critical role in virus morphogenesis. This protein is a 63 amino acid membrane spanning protein which locates itself in the endoplasmic reticulum. Cleavage of p7 is mediated by the endoplasmic reticulum's signal peptidases.
5976145
Hepacivirus C


Two transmembrane domains of p7 are connected by a cytoplasmic loop and are oriented towards the endoplasmic reticulum's lumen. NS2 protein is a 21–23 kiloDalton (kDa) transmembrane protein with protease activity. NS3 is 67 kDa protein whose N-terminal has serine protease activity and whose C-terminal has NTPase/helicase activity. It is located within the endoplasmic reticulum and forms a heterodimeric complex with NS4A—a 54 amino acid membrane protein that acts as a cofactor of the proteinase. NS4B is a small (27 kDa) hydrophobic integral
5976146
Chloroplast


outermost of which is continuous with the rough endoplasmic reticulum. They synthesize ordinary starch, which is stored in granules found in the periplastid space—outside the original double membrane, in the place that corresponds to the red alga's cytoplasm. Inside cryptophyte chloroplasts is a pyrenoid and thylakoids in stacks of two. Their chloroplasts do not have phycobilisomes, but they do have phycobilin pigments which they keep in their thylakoid space, rather than anchored on the outside of their thylakoid membranes. Cryptophytes may have played a key role in the spreading
6481767
Murine polyomavirus


but at least VP2 has been reported to be exposed upon endocytosis of the viral particle and may be involved in releasing the virus from the endoplasmic reticulum. MPyV has been reported to enter cells through both a caveolae-dependent endocytosis mechanism and by an independent mechanism through uncoated vesicles. Unlike many viruses that enter the cell through endocytosis, polyomaviruses penetrate the cell membrane and enter the cytosol from the late endoplasmic reticulum rather than from endosomes, although conformational changes in response to low pH in endolysosomes have been hypothesized as critical steps in the
13590816
Glucose 6-phosphate


to travel to other places in the body. Liver cells express the transmembrane enzyme glucose-6-phosphatase in the endoplasmic reticulum. The catalytic site is found on the lumenal face of the membrane, and removes the phosphate group from glucose-6-phosphate produced during glycogenolysis or gluconeogenesis. Free glucose is transported out of the endoplasmic reticulum via GLUT7 and released into the bloodstream via GLUT2 for uptake by other cells. Muscle cells lack this enzyme, so myofibers use glucose-6-phosphate in their own metabolic pathways such as glycolysis. Importantly, this prevents myocytes from releasing glycogen stores they
6771229
Auriscalpium vulgare


bodies containing electron-opaque inclusions are set within gaps on opposite ends of the nuclear membrane. This membrane has occasional gaps but is largely continuous. Fragments of endoplasmic reticulum occur near the spindle pole bodies, but do not form a cap. "Auriscalpium vulgare" can be grown in pure culture on agar-containing plates supplemented with nutrients. The colonies that grow are white to pale cream, and cover the agar surface within six weeks from the initial inoculation. The mycelium is made of bent-over hyphae, without any
2468137
Endoplasm


molecules like carbohydrates, then are sent to the Golgi apparatus, where they are further modified and packaged to be sent to their final destination. Vesicles are responsible for transport in between components of the endomembrane system and the plasma membrane. In addition to these 2 main processes, there are many other activities that take place in the endoplasm. Lysosomes degrade waste and toxins with the enzymes they contain. Smooth endoplasmic reticulum makes hormones and lipids, degrades toxins, and controls cellular levels of calcium. Though most control of cell division is
19623978
Microvesicles


within the vesicles and their plasma membranes. Both the membrane molecular pattern and the internal contents of the vesicle depend on the cellular origin and the molecular processes triggering their formation. Because microvesicles are not intact cells, they do not contain mitochondria, Golgi, endoplasmic reticulum, or a nucleus with its associated DNA. Microvesicle membranes consist mainly of membrane lipids and membrane proteins. Regardless of their cell type of origin, nearly all microvesicles contain proteins involved in membrane transport and fusion. They are surrounded by a phospholipid bilayer composed of several
10330120
Mitochondrion


and fatty acid Co-A ligase. Disruption of the outer membrane permits proteins in the intermembrane space to leak into the cytosol, leading to certain cell death. The mitochondrial outer membrane can associate with the endoplasmic reticulum (ER) membrane, in a structure called MAM (mitochondria-associated ER-membrane). This is important in the ER-mitochondria calcium signaling and is involved in the transfer of lipids between the ER and mitochondria. Outside the outer membrane there are small (diameter: 60Å) particles named sub-
19833189
Mitochondria associated membranes


form auto-phagosomes. These closed membranes are double membrane-bond, with lysosomes inside it. The main function of these membrane is degradation, as role in cellular homeostasis. However, the origin of them has remained unclear. Maybe it is the plasma membrane, the endoplasmic reticulum (ER) and the mitochondria. But the ER- mitochondria contact site have markers, the auto-phagosome marker ATG14, and the auto-phagosome-formation marker ATG5, until the formation of auto-phagosome is complete. Whereas, the
8723356
Eukaryote


a process of endocytosis, where the outer membrane invaginates and then pinches off to form a vesicle. It is probable that most other membrane-bound organelles are ultimately derived from such vesicles. Alternatively some products produced by the cell can leave in a vesicle through exocytosis. The nucleus is surrounded by a double membrane (commonly referred to as a nuclear membrane or nuclear envelope), with pores that allow material to move in and out. Various tube- and sheet-like extensions of the nuclear membrane form the endoplasmic reticulum, which
16087413
TMEM242


. The two transmembrane domains have alpha helices. These helices are formed from uncharged residues that are buried in the membrane. These helices are not exposed for binding. Other parts of the tmem242 protein may form secondary structures. The tmem242 protein further folds to its final structure to embed in a membrane. It is likely tmem242 is embedded in the cellular membrane, there is also potential for tmem242 to embed in the mitochondrial membrane or the endoplasmic reticulum membrane. Tmem242 undergoes various post-translational modification. There are 11 serine residues that
5746850
Endomembrane system


The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryotes the organelles of the endomembrane system include: the nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes, and plasma (cell) membrane among others. The system is defined more accurately as the set of membranes that form a single functional and developmental unit, either being connected directly, or exchanging material through
9903429
Sarcoplasmic reticulum


The sarcoplasmic reticulum (SR) is a membrane-bound structure found within muscle cells that is similar to the endoplasmic reticulum in other cells. The main function of the SR is to store calcium ions (Ca). Calcium ion levels are kept relatively constant, with the concentration of calcium ions within a cell being 100,000 times smaller than the concentration of calcium ions outside the cell. This means that small increases in calcium ions within the cell are easily detected and can bring about important cellular changes (the calcium is said to
797521
Positive-sense single-stranded RNA virus


viral genome to viral replication complexes (VRCs) formed in association with intracellular membranes. VRCs contain proteins of both viral and host cell origin, and may be associated with the membranes of a variety of organelles, often the rough endoplasmic reticulum, but also including membranes derived from mitochondria, vacuoles, the Golgi apparatus, chloroplasts, peroxisomes, plasma membranes, autophagosomal membranes, and novel cytoplasmic compartments. The replication of the positive-sense ssRNA genome proceeds through double-stranded RNA intermediates, and the purpose of replication in these membranous
12818648
Nuclear envelope


the nuclear lamina, a mesh of intermediate filaments which stabilizes the nuclear membrane as well as being involved in chromatin function and entire expression. It is connected to the outer membrane by nuclear pores which penetrate the membranes. While the two membranes and the endoplasmic reticulum are linked, proteins embedded in the membranes tend to stay put rather than dispersing across the continuum. It is lined with a fiber network called as nuclear lamina which is 10-40 nm thick and provide strength. Mutations in the inner nuclear membrane proteins can cause several
21175986
Connexin


regulated physiological processes to take place, such as in the myometrium. As they are being translated by ribosomes, connexins are inserted into the membrane of the endoplasmic reticulum (ER). It is in the ER that connexins are properly folded, yielding two extracellular loops, EL-1 and EL-2. It is also in the ER that the oligomerization of connexin molecules into hemichannels begins, a process which may continue in the UR-Golgi intermediate compartment as well. The arrangements of these hemichannels can be homotypic, heterotypic, and combined heterotypic
9478623