Fat facets interacts with vasa in the Drosophila pole plasm and protects it from degradation.

Anterior-posterior patterning and germ cell specification in Drosophila requires the establishment, during oogenesis, of a specialized cytoplasmic region termed the pole plasm. Numerous RNAs and proteins accumulate to the pole plasm and assemble in polar granules. Translation of some of these RNAs is generally repressed and active only in pole plasm. Vasa (VAS) protein, an RNA helicase and a component of polar granules, is essential maternally for posterior patterning and germ cell specification, and VAS is a candidate translational activator in the pole plasm. VAS is stabilized within the pole plasm in that it is initially present throughout the entire embryo but strictly limited to the pole cells by the cellular blastoderm stage. hsp83 mRNA, which accumulates in the pole plasm through a stabilization-degradation mechanism, is another example. Here, we used a biochemical approach to identify proteins that copurify with VAS in crosslinked extracts. Prominent among these proteins was the ubiquitin-specific protease Fat facets (FAF), a pole plasm component [7], but one whose roles in posterior patterning and germ line specification have remained unclear. We present evidence that FAF interacts with VAS physically and reverses VAS ubiquitination, thereby stabilizing VAS in the pole plasm.