FIGURE 10-31 Model for control of cytoplasmic polyadenylation and translation initiation. (Left) In immature oocytes, mRNAs containing the U-rich cytoplasmic polyadenylation element (CPE) have short poly(A) tails. CPE-binding protein (CPEB) mediates repression of translation through the interactions depicted, which prevent assembly of an initiation complex at the 5′ end of the mRNA. (Right) Hormonal stimulation of oocytes activates a protein kinase that phosphorylates CPEB, causing it to release Maskin. The cleavage and polyadenylation specificity factor (CPSF) then binds to the poly(A) site, interacting with both bound CPEB and the cytoplasmic form of poly(A) polymerase (PAP). After the poly(A) tail is lengthened, multiple copies of cytoplasmic poly(A)-binding protein 1 (PABPC1) can bind to it and interact with eIF4G, which functions with other initiation factors to bind the 40S ribosomal subunit and initiate translation. See R. Mendez and J. D. Richter, 2001, Nat. Rev. Mol. Cell Biol. 2:521.