Sequence-specific RNA-binding protein that binds to the cytoplasmic polyadenylation element (CPE), an uridine-rich sequence element (consensus sequence 5'-UUUUUAU-3') within the mRNA 3'-UTR (PubMed:17024188). RNA binding results in a clear conformational change analogous to the Venus fly trap mechanism (By similarity). Regulates activation of unfolded protein response (UPR) in the process of adaptation to ER stress in liver, by maintaining translation of CPE-regulated mRNAs in conditions in which global protein synthesis is inhibited (PubMed:28092655). Required for cell cycle progression, specifically for cytokinesis and chromosomal segregation (By similarity). Plays a role as an oncogene promoting tumor growth and progression by positively regulating translation of t-plasminogen activator/PLAT (PubMed:22138752). Stimulates proliferation of melanocytes (By similarity). In contrast to CPEB1 and CPEB3, does not play role in synaptic plasticity, learning and memory (PubMed:24386439). Interacts with TOB1. Highly expressed in brain, including hippocampus, amygdala, granule and Purkinje cells of the cerebellum (at protein level) (PubMed:17024188, PubMed:24386439). Expressed in spinal cord (at protein level) (PubMed:27381259). Expressed in kidney, lung and heart (at protein level) (PubMed:12871996, PubMed:27381259, PubMed:24386439). Expressed in liver (at protein level) (PubMed:28092655, PubMed:12871996, PubMed:27381259, PubMed:24386439). Expressed in spleen and testis (at protein level) (PubMed:24386439, PubMed:12871996). Weakly expressed in ovary and in granular cells of dentate gyrus and the pyramidal cells of CA3 and CA1 of the hippocampus (PubMed:12871996). Highly expressed in developing brain, spinal cord and attached dorsal root ganglia (DRG) (at protein level). At embryonic day 18.5 expressed in gray matter of spinal cord, diencephalons, hippocampus and parts of midbrain and hindbrain. At postnatal day 20 expression persists in spinal cord and brain. Expressed in embryonic heart. Up-regulated in granular cells of the dentate gyrus of CA1 and CA3 after kainate-induced seizures (PubMed:12871996). Up-regulated by high-fat-diet and aging-induced endoplasmic reticulum stress (PubMed:28092655). Expression level fluctuation follows the circadian clock amplitude (PubMed:28092655). The 2 RRM domains and the C-terminal region mediate interaction with CPE-containing RNA. The interdomain linker (564-579) acts as a hinge to fix the relative orientation of the 2 RRMs. The ZZ domain (509-566) coordinates 2 Zn ions and is probably implicated in mediating interactions with other proteins in addition to increasing the affinity of the RRMs for the CPEs. Unlike in CPEB1, a continuous polar interface is formed between the 2 RRMs. No visible phenotype at young age or under unchallenged conditions (PubMed:24386439, PubMed:28092655). At 80 weeks or under high fat diet feeding conditions, mutant mice develop hepatosteatosis with excessive liver weight and accumulation of cytosolic lipid droplets sometimes accompanied by fibrosis (PubMed:28092655). Belongs to the RRM CPEB family.