THE DEADENYLATION CONFERRED BY THE 3' UNTRANSLATED REGION OF A DEVELOPMENTALLY CONTROLLED MESSENGER-RNA IN XENOPUS-EMBRYOS IS SWITCHED TO POLYADENYLATION BY DELETION OF A SHORT SEQUENCE ELEMENT

The maternal Xenopus Eg mRNAs are adenylated and translated in the mat ure oocyte and then, after fertilization, are deadenylated and release d from polysomes. Therefore, after fertilization, a change occurs in t he cellular mechanisms that control mRNA adenylation. In the study rep orted here, we show that the 3' untranslated region of Eg2 mRNA contai ns a cis-acting element that is required for the deadenylation of chim eric RNAs after fertilization. This cis-acting element is contained wi thin a single 17-nucleotide portion of the Eg2 mRNA. Disruption of thi s deadenylation element allows adenylation of the chimeric transcripts in the embryo. Therefore, this cis-acting element is part of the sequ ence information required for the developmental switch from adenylatio n to deadenylation of the maternal Eg2 mRNA in Xenopus embryos.