RNA recognition motif 2 (RRM2) found in cytoplasmic polyadenylation element-binding protein CPEB-2, CPEB-3, CPEB-4 and similar protiens
This subgroup corresponds to the RRM2 of the paralog proteins CPEB-2, CPEB-3 and CPEB-4, all well conserved in both, vertebrates and invertebrates. Due to the high sequence similarity, members in this family may share similar expression patterns and functions. CPEB-2 is an RNA-binding protein that is abundantly expressed in testis and localized in cytoplasm in transfected HeLa cells. It preferentially binds to poly(U) RNA oligomers and may regulate the translation of stored mRNAs during spermiogenesis. Moreover, CPEB-2 impedes target RNA translation at elongation; it directly interacts with the elongation factor, eEF2, to reduce eEF2/ribosome-activated GTP hydrolysis in vitro and inhibit peptide elongation of CPEB2-bound RNA in vivo. CPEB-3 is a sequence-specific translational regulatory protein that regulates translation in a polyadenylation-independent manner. It functions as a translational repressor that governs the synthesis of the AMPA receptor GluR2 through binding GluR2 mRNA. It also represses translation of a reporter RNA in transfected neurons and stimulates translation in response to NMDA. CPEB-4 is an RNA-binding protein that mediates meiotic mRNA cytoplasmic polyadenylation and translation. It is essential for neuron survival and present on the endoplasmic reticulum (ER). It is accumulated in the nucleus upon ischemia or the depletion of ER calcium. CPEB-4 is overexpressed in a large variety of tumors and is associated with many mRNAs in cancer cells. All family members contain an N-terminal unstructured region, two RNA recognition motifs (RRMs), also termed RBDs (RNA binding domains) or RNPs (ribonucleoprotein domains), and a Zn-finger motif. In addition, they do have conserved nuclear export signals that are not present in CPEB-1.