FIG. 4.

Effect of recB, recF, or recR mutations on cell viability after induction of mutant Y. pestis topoisomerase I. Arabinose (0.002%) was added to the exponential-phase cultures of BW27784, YT102, JHS2, and JHS3 transformed with pAYTOP-G122S. Viable cell counts of arabinose-treated cultures determined after different periods of incubation at 37°C were divided by viable cell counts from untreated cultures to determine the relative viability. The results represent the averages and standard deviations from three experiments.