Like most other flaviviruses,<unk> V is an enveloped virus with icosahedral symmetry. Electron microscope studies reveal a 45–50 nm virion covered with a relatively smooth protein shell; this structure is similar to the dengue fever virus, another Flavivirus. The protein shell is made of two structural proteins: the glycoprotein E and the small membrane protein M. Protein E has numerous functions including receptor binding, viral attachment, and entry into the cell through membrane fusion. The outer protein shell is covered by a host-derived lipid membrane, the viral envelope. The flavivirus lipid membrane has been found to contain cholesterol and phosphatidylserine, but other elements of the membrane have yet to be identified. The lipid membrane has many roles in viral infection, including acting as signaling molecules and enhancing entry into the cell. Cholesterol, in particular, plays an integral part in<unk> V entering a host cell. The two viral envelope proteins, E and M, are inserted into the membrane. The RNA genome is bound to capsid (C) proteins, which are 105 amino-acid residues long, to form the nucleocapsid. The capsid proteins are one of the first proteins created in an infected cell; the capsid protein is a structural protein whose main purpose is to package RNA into the developing viruses. The capsid has been found to prevent apoptosis by affecting the Akt pathway. Genome The<unk>  genome. Modified after Guzman et al. 2010.<unk> V is a positive-sense, single-stranded RNA virus. Its genome is approximately 11,000 nucleotides long and is flanked by 5′ and 3′ non-coding stem loop structures. The coding region of the genome codes for three structural proteins and seven nonstructural (NS) proteins, proteins that are not incorporated into the structure of new viruses. The<unk> V genome is first translated into a polyprotein and later cleaved by virus and host proteases into separate proteins (i.e. NS1, C, E). Structural proteins Structural proteins (C, prM/M, E) are capsid, precursor membrane proteins, and envelope proteins, respectively. The structural proteins are located at the 5′ end of the genome and are cleaved into mature proteins by both host and viral proteases. Structural Protein Function C Capsid protein; encloses the RNA genome, packages RNA into immature virions. prM/M Viruses with M protein are infectious: the presence of M protein allows for the activation of proteins involved in viral entry into the cell. prM (precursor membrane) protein is present on immature virions, by further cleavage by furin to M protein, the virions become infectious. E A glycoprotein that forms the viral envelope, binds to receptors on the host cell surface in order to enter the cell. Nonstructural proteins Nonstructural proteins consist of NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5. These proteins mainly assist with viral replication or act as proteases. The nonstructural proteins are located near the 3′ end of the genome. Nonstructural Protein Function NS1 NS1 is a cofactor for viral replication, specifically for regulation of the replication complex. NS2A NS2A has a variety of functions: it is involved in viral replication, virion assembly, and inducing host cell death. NS2B A cofactor for NS3 and together forms the NS2B-NS3 protease complex. Contains transmembrane domains which bind the protease to intracellular membranes. NS3 A serine protease that is responsible for cleaving the polyprotein to produce mature proteins; it also acts as a helicase. NS4A NS4A is a cofactor for viral replication, specifically regulates the activity of the NS3 helicase. NS4B Inhibits interferon signaling. NS5 The largest and most conserved protein of<unk> V, NS5 acts as a methyltransferase and a RNA polymerase, though it lacks proofreading properties.
West Nile virus
Western equine encephalitis virus
Venezuelan equine encephalitis virus
Dengue virus
Sepik virus
Rabies virus
Zika virus
Cricket paralysis virus