A Xenopus protein related to hnRNP I has a role in cytoplasmic RNA localization

Cytoplasmic localization of mRNA molecules is a powerful mechanism for gene rating cell polarity. II? vertebrates, one paradigm is localization of Vg1 RNA within the Xenopus oocyte, a process directed by recognition of a local ization element within the Vg1 3' UTR. We show that specific base changes w ithin the localization element abolish both localization in vivo and bindin g in vitro by a single protein, VgRBP60. VgRBP60 is homologous to a human h nRNP protein, hnRNP I, and combined immunolocalization and in situ hybridiz ation demonstrate striking colocalization of hnRNP I and Vg1 RNA within the vegetal cytoplasm of the Xenopus oocyte. These results implicate a novel r ole in cytoplasmic RNA transport for this family of nuclear RNA-binding pro teins.