Genetic studies have shown that Aubergine (Aub), one of the Piwi subfamily of 
Argonautes in Drosophila, is essential for germ cell formation and maintaining 
fertility. aub mutations lead to the accumulation of retrotransposons in ovaries 
and testes, and Stellate transcripts in testes. Aub in ovaries associates with a 
variety of Piwi-interacting RNAs (piRNAs) derived from repetitive intergenic 
elements including retrotransposons. Here we found that Aub in testes also 
associates with various kinds of piRNAs. Although in ovaries Aub-associated 
piRNA populations are quite diverse, piRNAs with Aub in testes show a strong 
bias. The most abundant piRNAs were those corresponding to antisense transcripts 
of Suppressor of Stellate [Su(Ste)] genes known to be involved in Stellate gene 
silencing. The second most abundant class was made up of those from chromosome X 
and showed strong complementarity to vasa transcripts. Immunopurified Aub-piRNA 
complexes from testes displayed activity in cleaving target RNA containing 
sequences complementary to Stellate and vasa transcripts. These results provide 
the first biochemical insights into gene silencing mechanisms mediated by Aub 
and piRNAs in fly testes.