Involvement of DNA end-binding protein Ku in Ty element retrotransposition

Saccharomyces cerevisiae Ty elements are retrotransposons whose life cycles are strikingly similar to those of retroviruses. They transpose via an RNA intermediate that is converted to linear double-stranded cDNA and then ins erted into the host genome. Although Ty integration is mediated by the elem ent-encoded integrase, it has been proposed that host factors are involved in this process. Here we show that the DNA end-binding protein Ku, which fu nctions in DNA double-strand break repair, potentiates retrotransposition. Specifically, by using a galactose-inducible Ty1 system, we found that in v ivo, Ty1 retrotransposition rates were substantially reduced in the absence of Ku. In contrast, this phenotype was not observed with yeast strains con taining mutations in other genes that are involved in DNA repair. We presen t evidence that Ku associates with Ty1 viruslike particles both in vitro an d in vivo. These results provide an additional role for Ku and suggest that it might function in the life cycles of retroelements in other systems.