recA+-dependent inactivation of the lambda repressor in Escherichia coli lysogens by gamma-radiation and by tif expression.

When gamma lysogens of E. coli are induced by gamma-radiation the gamma repressor, as measured by its specific binding to gamma DNA, is rapidly inactivated by a recA+-dependent process which does not require new protein synthesis. This rapid inactivation is similar to inactivation of repressor by expression of the temperature sensitive E. coli mutation tif. In contrast, induction by UV irradiation or mitomycin C treatment requires new protein synthesis and there is a lag before the repressor is inactivated (Tomizawa and Ogawa, 1967; Shinagawa and Itoh, 1973).