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Reversion studies with exrB in Escherichia coli
Published online by Cambridge University Press: 14 April 2009
Summary
exrB derivatives of H/r30 and WP2 are sensitive to ultraviolet radiation (UV), methylmethane sulphonate (MMS) and will not form colonies at 42 °C. Revertants to wild type were selected by plating on either nutrient plates containing MMS or nutrient plates incubated at 42 °C. Revertants selected for MMS resistance were temperature- and UV-resistant, and all revertants selected for temperature resistance were MMS and UV resistant. The frequency with which revertants appeared on MMS plates was about eight times as high as it was at 42 °C, and the variance in frequency of revertants among cultures started with small inocula was higher on selection at 42 °C than on MMS. The spontaneous frequency was estimated to be 10−6 to 10−7, sufficiently low to suggest a single mutational event. Among wild-type revertants selected at 42 °C there was a stable and an unstable class. exrB+ could be co-transduced with malB+ from stable revertants to an exrB strain, but could not from unstable revertants. None of the revertants could support the growth of amber or ochre mutants of phage T4, nor were amber and ochre suppressed exrB strains wild type with regards MMS and temperature resistance. The presence of a polarity suppressor in an exrB strain did not modify resistance to UV or temperature. Neither UV or MMS was able to induce mutations in an exrB strain.
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- Copyright © Cambridge University Press 1975
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