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

ABSTRACT

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 region of the vitellogenin mRNA 3'-untranslated region (3'-UTR) implicated in estrogen-mediated stabilization. The vigilin-binding site in the vitellogenin B1 mRNA 3'-UTR contains two consensus PMR-1 cleavage sites. The availability of purified PMR-1 and recombinant vigilin made it possible to test the hypothesis that RNA-binding proteins interact with cis-acting elements to stabilize target mRNAs by blocking cleavage by site-specific mRNA endonucleases. Vigilin binds to the vitellogenin mRNA 3'-UTR site with at least 30-fold higher affinity than it exhibits for the albumin mRNA segment containing the mapped PMR-1 cleavage sites. This differential binding affinity correlates with differential in vitro susceptibility of the protein-RNA complexes to cleavage by PMR-1. Whereas recombinant vigilin has no detectable protective effect on PMR-1 cleavage of albumin mRNA, it retards in vitro cleavage of the vitellogenin mRNA 3'-UTR by purified PMR-1. The PMR-1 sites in the vitellogenin mRNA 3'-UTR are functional because they are readily cleaved in vitro by purified PMR-1. These results provide direct evidence for differential susceptibility to endonuclease-mediated mRNA decay resulting from the differential affinity of a RNA-binding protein for cis-acting stability determinants.