Translational control poly(A) elongation during Xenopus development: Differential repression and enhancement by a novel cytoplasmic polyadenylation element

One characteristic of oocyte maturation and embryogenesis in Xenopus laevis is the activation of translationally repressed (masked) maternal mRNAs by cytoplasmic poly(A) elongation. At maturation, poly(A) elongation is controlled by two cis-acting elements in the 3'-untranslated regions (UTRs) of responsive mRNAs, the hexanucleotide AAUAAA and the cytoplasmic polyadenylation element (CPE), consisting of UUUUUAU or other similar sequences. To investigate poly(A) elongation and translational activation during embryogenesis, we have focused on Cl2 RNA, a representative transcript that undergoes these processes. We show that precocious poly(A) elongation of Cl2 RNA during oocyte maturation is prevented by a large "masking" element that includes the dodecauridine CPE. The dual role of the CPE in both repression and activation of poly(A) elongation is discussed.