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

The interaction trap method was used to isolate putative binding partners o f Rad16/PsoS, a protein responsible for repair of silent DNA. One of the in teractors found was Sgs1, a DNA helicase influencing the life span of Sacch aromyces cerevisiae, with homology to the human BLM, WRN and RECQL4 protein s. Using the same fusion proteins from the two-hybrid screening, we show ev idence that both proteins also interact in vitro. We tested isogenic strain s, containing mutant alleles of the two genes in single and double mutant c ombination, for phenotypic similarity. Life span in sgs1 Delta single and s gs1 Delta rad16 Delta double mutants is about 40% of that of WT, and the ra d16/pso5 Delta single mutant also had its life span reduced to 75%. Sensiti vity to different mutagens, whose lesions are poorly repaired in rad16/pro5 Delta mutants, was tested in sgs1 Delta mutants. The sgs1 Delta conferred sensitivity to MMS, H2O2 and was moderately sensitive to UV254nm (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 d amage. (C) 2001 Elsevier Science B.V All tights reserved.