VASA localization requires the SPRY-domain and SOCS-box containing protein, GUSTAVUS.

VASA (VAS), a key protein in establishing the specialized translational activity of the Drosophila pole plasm, accumulates at the posterior pole of the developing oocyte. We identified a gene, gustavus (gus), that encodes a protein that interacts with VAS. A gus mutation blocks posterior localization of VAS, as does deletion of a segment of VAS containing the GUS binding site. Like VAS, GUS is present in cytoplasmic ribonucleoprotein particles. Heterozygotes for gus or a deletion including gus produce embryos with fewer pole cells and posterior patterning defects. Therefore, GUS is essential for the posterior localization of VAS. However, gus is not required for the posterior localization of oskar (osk). Apparent gus orthologs are present in mammalian genomes.