RNA-BINDING PROTEIN CONSERVED IN BOTH MICROTUBULE-BASED AND MICROFILAMENT-BASED RNA LOCALIZATION

Vg1 mRNA translocation to the vegetal cortex of Xenopus oocytes requir es intact microtubules, and a 3' UTR cia-acting element (termed VLE), which also mediates sequence-specific binding of several proteins. One protein, the 69-kD Vg1 REP, associates Vg1 RNA to microtubules in vit ro. Here we show that Vg1 REP-binding sites correlate with vegetal loc alization. Purification and cloning of Vg1 REP revealed five RNA-bindi ng motifs: four KH and one RRM domains. Surprisingly, Vg1 REP is highl y homologous to the zipcode binding protein implicated in the microfil ament-mediated localization of beta actin mRNA in fibroblasts. These d ata support Vg1 RBP's direct role in vegetal localization and suggest the existence of a general, evolutionarily conserved mechanism for mRN A targeting.