Interaction of the yeast Pso5/Rad16 and Sgs1 proteins: influences on DNA repair and aging

Abstract

The interaction trap method was used to isolate putative binding partners of Rad16/Pso5, a protein responsible for repair of silent DNA. One of the interactors found was Sgs1, a DNA helicase influencing the life span of Saccharomyces cerevisiae, with homology to the human BLM, WRN and RECQL4 proteins. Using the same fusion proteins from the two-hybrid screening, we show evidence that both proteins also interact in vitro. We tested isogenic strains, containing mutant alleles of the two genes in single and double mutant combination, for phenotypic similarity. Life span in sgs1Δ single and sgs1Δ rad16Δ double mutants is about 40% of that of WT, and the rad16/pso5Δ single mutant also had its life span reduced to 75%. Sensitivity to different mutagens, whose lesions are poorly repaired in rad16/pso5Δ mutants, was tested in sgs1Δ mutants. The sgs1Δ conferred sensitivity to MMS, H₂O₂ and was moderately sensitive to UV_254 nm (UVC) and 4-NQO. An epistatic interaction between rad16 and sgs1 mutations after UVC, 4-NQO and H₂O₂ was observed. Moreover, we found that in a top3 background, functional Sgs1p and Rad16p apparently channel MMS, 4-NQO and H₂O₂ induced lesions into aberrant DNA repair. Our results demonstrate that Sgs1 is not only involved in genome stability, somatic recombination and aging, but is also implicated, together with Rad16/Pso5, in the repair of specific DNA damage.