text: <unk>  (cAMP response element-binding) proteins are transcription factors which bind to certain sequences called cAMP response elements (CRE) in DNA and thereby increase or decrease the transcription of certain genes.<unk>  is highly related (in structure and function) to CREM (cAMP response element modulator) and ATF-1 (activating transcription factor-1) proteins.<unk>  proteins are active in many animals, including humans. The typical (somewhat simplified) sequence of events is as follows: a signal arrives at the cell surface, activates the corresponding receptor, which leads to the production of a second messenger such as cAMP or Ca2+, which in turn activates a protein kinase. This protein kinase moves to the cell nucleus, where it activates a<unk>  protein. The activated<unk>  protein then binds to a CRE region, and is then bound to by a CBP <unk>  binding protein) which coactivates it, allowing it to switch certain genes on or off. The DNA binding of<unk>  is mediated via its basic leucine zipper domain (bZIP domain) as depicted in the picture.<unk>  has many functions in many different organs although most of its functions have been studied in relation to the brain.<unk>  proteins in neurons are thought to be involved in the formation of long-term memories; this has been shown in the marine snail Aplysia, the fruit fly Drosophila melanogaster, and in rats. They are necessary for the late stage of long term potentiation. There are activator and repressor forms of<unk> . Flies genetically engineered to overexpress the inactive form of<unk>  lose their ability to retain long term memory.<unk>  is also important for the survival of neurons, as shown in genetically engineered mice, where<unk>  and CREM were deleted in the brain. This study supports the view that disturbance of<unk>  function in brain can contribute to the development and progression of Huntington's Disease in humans. If<unk>  is lost in the whole developing mouse embryo, the mice die immediately after birth, again highlighting the critical role of<unk>  in promoting survival.<unk>  is also thought to be involved in the growth of some types of cancer.
  In humans, abnormalities of a protein which interacts with the KID domain of<unk> , the<unk>  binding protein (CBP) is associated with Rubinstein-Taybi syndrome.
option_0: CREB
option_1: AKT
option_2: APC 
option_3: PCNA
option_4: Ras 
option_5: Ras
option_6: Rho
option_7: XMC