Fig. 3.

In vivo CPT sensitivity assay of S. cerevisiae expressing Top1. Five microliters of 10-fold serial dilutions (indicated by triangles) of Top1-deleted yeast cells harboring the plasmid encoding plant Top1s (A) or OjTop1 and its mutants (B) were spotted on plates. The expression of exogenous Top1 was induced by galactose and repressed by glucose. The galactose plates were supplemented with 0.25% Me₂SO or 5 μg/ml CPT in a final Me₂SO concentration of 0.25%. After incubation at 30°C for 2 days, the cell growth was scored as follows: S, CPT-sensitive Top1; S/r, partially CPT-resistant Top1; R, CPT-resistant Top1.