Vigilin binding selectively inhibits cleavage of the vitellogenin mRNA 3 '-untranslated region by the mRNA endonuclease polysomal ribonuclease 1

In Xenopus, estrogen induces the stabilization of vitellogenin mRNA and the destabilization of albumin mRNA. These processes correlate with increased polysomal activity of a sequence-selective mRNA endonuclease, PMR-1, and a hnRNP K homology-domain RNA-binding protein, vigilin. Vigilin binds to a re gion of the vitellogenin mRNA 3'-untranslated region (3'-UTR) implicated in estrogen-mediated stabilization. The vigilin-binding site in the vitelloge nin B1 mRNA 3'-UTR contains two consensus PMR-1 cleavage sites. The availab ility of purified PMR-1 and recombinant vigilin made it possible to test th e hypothesis that RNA-binding proteins interact with cis-acting elements to stabilize target mRNAs by blocking cleavage by site-specific mRNA endonucl eases. Vigilin binds to the vitellogenin mRNA 3'-UTR site with at least 30- fold higher affinity than it exhibits for the albumin mRNA segment containi ng the mapped PMR-1 cleavage sites. This differential binding affinity corr elates with differential in vitro susceptibility of the protein-RNA complex es to cleavage by PMR-1. Whereas recombinant vigilin has no detectable prot ective effect on PMR-1 cleavage of albumin mRNA, it retards in vitro cleava ge of the vitellogenin mRNA 3'-UTR by purified PM R-l. The PMR-1 sites in t he vitellogenin mRNA 3'-UTR are functional because they are readily cleaved in vitro by purified PMR-1. These results provide direct evidence for diff erential susceptibility to endonuclease-mediated mRNA decay resulting from the differential affinity of a RNA-binding protein for cis-acting stability determinants.