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Vg1 RNA-binding protein (RBP) play a direct role in vegetal localization and this implies the existence of a general mechanism for mRNA targeting. Five RNa binding motifs were found in purified and cloned Vg1 RBPs. The experiments are explained in detail. Vg1 RBP is homologous to ZBP-1, a protein associated with mRNA targeting in fibroblasts. There are, however, important differences also.

The Xenopus Vg1 mRNA is a transforming growth factor which remains localized to the vegetal cortex of late-stage oocytes until after gastrulation. An investigation was conducted to determine the cis- and trans-acting factors involved in Vg1 mRNA vegetal cortex localization. Competition experiments identified two protein binding regions in the 3' untranslated region (UTR) which are involved in vegetal localization. In addition, a 69-kDa protein which binds to this region was identified. These results suggest the involvement of the 3' UTR signals and cellular factors which recognize these signals in mRNA oocyte localization.