Vigilin, a ubiquitous protein with 14 K homology domains, is the estrogen-inducible vitellogenin mRNA 3'-untranslated region-binding protein.

RNA-binding proteins containing KH domains are widely distributed. One KH domain protein of unknown function, vigilin (also known as the high density lipoprotein-binding protein), contains 14 KH domains and is ubiquitous in vertebrate cells. We previously used RNA gel mobility shift assays to describe an estrogen-inducible protein which binds specifically to a segment of the 3'-untranslated region (3'-UTR) of vitellogenin mRNA, an area which has been implicated in the estrogen-mediated stabilization of vitellogenin mRNA. Here we show that the vitellogenin mRNA-binding protein (VitRNABP) is vigilin. The VitRNABP was isolated as a 150-155-kDa protein on a vitellogenin mRNA 3'-UTR affinity column. Peptide microsequencing revealed that the purified protein was vigilin, a conclusion confirmed in Western blot analysis with antibodies to vigilin. Direct confirmation that vigilin is the VitRNABP was obtained from RNA gel mobility shift assays which demonstrated that antibodies to chicken vigilin supershifted the Xenopus VitRNABP band. Xenopus liver vigilin mRNA and the VitRNABP exhibited similar induction by estrogen, providing additional confirmation that vigilin is the estrogen-inducible protein which binds to the 3'-UTR of estrogen-stabilized vitellogenin mRNA. These data support a role for vigilin in the hormonal control of mRNA metabolism.