CPEB, or cytoplasmic polyadenylation element binding protein, is a highly conserved RNA-binding protein that promotes the elongation of the polyadenine tail of messenger RNA.[1] CPEB most commonly activates the target RNA for translation, but can also act as a repressor,[2] dependent on its phosphorylation state.[3] In animals, CPEB is expressed in several alternative splicing isoforms that are specific to particular tissues and functions, including the self-cleaving Mammalian CPEB3 ribozyme. CPEB was first identified in Xenopus oocytes and associated with meiosis;[1] a role has also been identified in the spermatogenesis of Caenorhabditis elegans.[4]
Drosophila Orb2 binds to genes implicated in long-term memory. An isoform of CPEB found in the neurons of the sea slug Aplysia californica, as well as in Drosophila, mice, and humans, contains an N-terminal domain not found in other isoforms that shows high sequence similarity to prion proteins. Experiments with the Aplysia isoform expressed in yeast reveal that CPEB has a key property associated with prions: it can cause other proteins to assume alternate protein conformations that are heritable in successive generations of yeast cells. Furthermore, the functional RNA-binding form of the CPEB protein may be the prion-like state.[5] These observations have led to the suggestion that long-lasting bistable prionlike proteins play a role in the formation of long-term memory.[6]
Key Contribution of CPEB4-mediated translational control to cancer progression. Elena Ortiz-Zapater et al, Nature Medicine, 4 December 2011 Nature Medicine doi:10.1038/nm.2540