FIG. 1.

Spontaneous forward mutation frequencies to rifampin resistance in E. coli base excision repair mutants. Mid-log-phase cultures were plated on Luria-Bertani medium with or without 100 μg of rifampin per ml and incubated for 15 h at 37°C. Mutants per 10⁸ cells are shown. The data represent the average of the three experiments summarized in Table 1. W.T., wild type.