CPEB

CPEB, or <a href="/facts/Cytoplasmic_polyadenylation_element/66xBhHDN">cytoplasmic polyadenylation element</a> binding protein, is a highly <a href="/facts/Conserved_sequence/YAxy2Xa2">conserved</a> <a href="/facts/RNA/HxPeNfNj">RNA</a>-binding <a href="/facts/Protein/Jxmagu3E">protein</a> that promotes the elongation of the <a href="/facts/Polyadenylation/ILnXUBKP">polyadenine tail</a> of <a href="/facts/Messenger_RNA/oUL6qxQn">messenger RNA</a>. CPEB is present at postsynaptic sites and dendrites where it stimulates polyadenylation and translation in response to synaptic activity. CPEB most commonly activates the target RNA for <a href="/facts/Translation_(genetics)/JcPC1rth">translation</a>, but can also act as a repressor, dependent on its <a href="/facts/Phosphorylation/LXUEEeIL">phosphorylation</a> state. As a repressor, CPEB interacts with the deadenylation complex and shortens the polyadenine tail of mRNAs. In animals, CPEB is expressed in several <a href="/facts/Alternative_splicing/nNRwPVNK">alternative splicing</a> isoforms that are specific to particular tissues and functions, including the self-cleaving <a href="/facts/Mammalian_CPEB3_ribozyme/SrTqjNU5">Mammalian CPEB3 ribozyme</a>. CPEB was first identified in <a href="/facts/Xenopus/AfAtcsyA">Xenopus</a> <a href="/facts/Oocyte/aYrWtc3n">oocytes</a> and associated with <a href="/facts/Meiosis/Pj5Q6nGN">meiosis</a>; a role has also been identified in the <a href="/facts/Spermatogenesis/8u8XNEV6">spermatogenesis</a> of <a href="/facts/Caenorhabditis_elegans/XJVJzPn2">Caenorhabditis elegans</a>.
CPEB is involved in closed-loop regulation of mRNAs that keeps them inactive. The closed-loop structure between the <a href="/facts/3%27UTR/wB0oYfKd">3'UTR</a> and <a href="/facts/5%27UTR/xv930kS8">5'UTR</a> inhibits translation. This has been observed in <a href="/facts/Xenopus_laevis/khG1KPrd">Xenopus laevis</a> in which <a href="/facts/EIF4E/FLMQ8Nc6">eIF4E</a> bound to the <a href="/facts/5%27_cap/cWUeEBJ6">5' cap</a> interacts with Maskin bound to CPEB on the <a href="/facts/3%27_UTR/wB0oYfKd">3' UTR</a> creating translationally inactive <a href="/facts/MRNA/oUL6qxQn">transcripts</a>. This translational inhibition is lifted once CPEB is <a href="/facts/Phosphorylated/LXUEEeIL">phosphorylated</a>, displacing the Maskin binding site, allowing for the <a href="/facts/Polymerization/1hmBz7Ur">polymerization</a> of the <a href="/facts/PolyA_tail/ILnXUBKP">PolyA tail</a>, which can recruit the translational machinery by means of <a href="/facts/PolyA-binding_protein/GKBfnzJK">PABP</a>. However, is important to note that this mechanism has been under great scrutiny.
CPEB has been shown to shuttle between the nucleus and <a href="/facts/Cytoplasm/Wa0sE6xf">cytoplasm</a>. In the nuclei of different organisms, it was found that CPEB helps guide the path of mRNA in the cytoplasm. CPEB was found to be almost exclusively in the c plasm in stage VI Xenopus oocytes. However, a further study on this topic found that there is a substantial amount of CPEB in the nucleus. CPEB can bind with CPE-containing mRNAs in the nucleus, which forces tight <a href="/facts/Translational_regulation/5gz1PL2a">translational regulation</a> in the cytoplasm. CPEBs bound to these mRNAs were found to have a lower translation efficiency, which is indicative of the translation regulation.

CPEB open-in-new

CPEB