FIG. 2.
top3Δ cells are sensitive to DNA-damaging agents. (a and b) Strains RKC1d (wild type; □), JMK22d (sgs1; ▪), RKC1c (sgs1 top3; ●), and RKC1a (top3; ○) were grown to early log phase in YPD medium and then exposed to either MMS (a) or UV (b), and percent survival was determined. The means and standard errors of three independent experiments are shown. (c) Tenfold serial dilutions of exponentially growing yeast cultures from wild-type cells harboring an empty vector, a top3Δ strain harboring an empty vector, or a top3Δ strain harboring plasmid-encoded TOP3 (pTOP3), as indicated on the left. The cells on the upper plate were untreated, those on the middle plate were treated with 0.01% MMS, and those on the lower plate were irradiated with 60 J of UV light/m2, as indicated on the right.