VgRBP71 stimulates cleavage at a polyadenylation signal in Vg1 mRNA,resulting in the removal of a cis-acting element that represses translation

Translation of Vg1 mRNA is repressed in Xenopus oocytes until it is localized to the vegetal cortex. Localization and translational repression are mediated by separate elements in the 3'UTR of the mRNA. VgRBP71 binds to the 3' end of the localization element and stimulates cleavage at an adjacent polyadenylation signal. The protein has an RNA strand-separation activity that likely underlies this event. Polyadenylation occurs at this site in Vg1 mRNA with the consequence of removing the downstream translational repressor element. Ectopic expression of VgRBP71 in stage II oocytes results in cleavage of the mRNA and premature expression of Vg1 protein. These results support a model in which VgRBP71 activates translation of Vg1 mRNA by promoting the removal of a cis-acting repressor element.