Involvement of DNA End-Binding Protein Ku in Ty Element Retrotransposition

Abstract

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 inserted into the host genome. Although Ty integration is mediated by the element-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 functions in DNA double-strand break repair, potentiates retrotransposition. Specifically, by using a galactose-inducible Ty1 system, we found that in vivo, Ty1 retrotransposition rates were substantially reduced in the absence of Ku. In contrast, this phenotype was not observed with yeast strains containing mutations in other genes that are involved in DNA repair. We present evidence that Ku associates with Ty1 viruslike particles both in vitro and 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.

ACKNOWLEDGMENTS

We thank H. Feldmann and E. L. Winnacker for providing us with the W303α and YKU70/HDF1-disrupted yeast strains, D. Weaver for the RAD52 knockout construct, I. Hickson for the SGS1 knockout construct, S. Hwang-Teo for the LIG4 knockout construct, S. Buratowski for pJA51 and pJA52, S. Elledge for Y661-based strains, J. Boeke for monoclonal antibody 8B11, J. Curcio for strain JC297, and D. J. Garfinkel for pGTyH3m HIS3AI and pGTy1-in2600. Thanks also to L. Yieh, S. Sandmeyer, and members of the S.P.J. lab, particularly Steve Bell, for helpful discussions.

This work was funded by grants SP2143/0102 and SP2143/0401 from The Cancer Research Campaign (UK).