Selective ploidy ablation, a high-throughput plasmid transfer protocol, identifies new genes affecting topoisomerase I–induced DNA damage

Top1 accumulates in vps25 cells, and accumulation is suppressed by removing the SUMOylation sites from Top1. (A) Fluorescence (YFP) and differential interference contrast (DIC) images are shown from wild-type (W9471-8C) and vps25▵ (W8842-5C) cells transformed with expression vectors containing YFP-TOP1 or the YFP-top1-K_65,91,92R (YFP-Top1-KR) mutant after a 4-h induction with 100 μM CuSO4. (B) Fluorescence signals were quantified using Volocity as described in the Methods. Protein levels from 50 to 120 individual cells of each strain were quantified, and the mean value for each strain was plotted in arbitrary units. Error bars indicate 95% confidence intervals. The asterisk indicates a significant difference between YFP-Top1 and YFP-Top1-KR fluorescence in a vps25▵ strain (P = 0.0004).