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. 1999 Jun;63(2):446–456. doi: 10.1128/mmbr.63.2.446-456.1999

FIG. 3.

FIG. 3

Essential features of poly(A) addition and removal during Xenopus development. In oocytes, CPEB binds the CPE and shifts an equilibrium between poly(A) tail growth or removal in the direction of growth. For mRNAs that do not contain a CPE, the equilibrium is shifted toward poly(A) tail removal, which is often referred to as default deadenylation. The enzyme responsible for deadenylation is PARN. HNBF refers to hexanucleotide binding factor. During embryogenesis, poly(A) tail elongation is directed by an embryonic-type CPE (eCPE), which is oligo(U)12–27. The eCPE is bond by the protein elrA, a member of the ELAV family of RNA binding proteins. In contrast to oocyte maturation, deadenylation in embryos is directed by the EDEN cis element. The EDEN sequence is bound by the protein EDEN-BP, which may interact, directly or indirectly, with PARN.