Fig. 1.

Lack of RNase H activities predominantly affects nucleolar DNA stability. (A) Tenfold serial dilutions of cells grown for 3 d on YPAD (control) or YPAD-containing 10 μg/mL CPT. (B) Rad52-YFP foci represent DNA repair centers associated to nuclear versus nucleolar DNA (rDNA; hatched). Nop1-mRFP was used as nucleolar marker. (Scale bars, 2.5 µm.) Percentage of cells containing Rad52-YFP foci counted in exponentially growing cells growing in the absence (control) or presence of CPT (10 µg/mL, 3-h treatment; Right). Data represent mean ± SD from three independent experiments. Note that the ratio of Rad52-YFP/Nop1-RFP colocalization increased from 29% (control) and 34% (+CPT) in WT cells to 61% (control) and 65% (+CPT) in r1∆ r2∆ mutants.