Figure 7.

Synergistic response of radA and DNA helicase/DNA pump mutants to DNA damage. Log phase cultures were diluted and plated on LB agar and then UV irradiated (A) or plated on LB medium containing the indicated concentration of AZT (B) or ciprofloxacin (C). Plates were incubated at 37°, and surviving colonies were counted after 18–36 hours. Experiments were performed on at least two different days. The mean fractional survival and standard deviation of at least eight independent cultures is shown. Dark gray bars show survival in wild type or radA strains, gray bars show survival in single DNA helicase mutant strains and light gray bars show survival in radA –DNA helicase double mutants. Fractional survival in the ruvAB strains on AZT could not be determined and was assigned a < 1 × 10⁻⁶ value as indicated.