Lysogenic induction of lambdoid phages in lexA mutants of Escherichia coli

Summary UV irradiation of lexA3 mutants of E. coli caused lysogenic induction of prophage , _i21, _i434 and 80. Maximal induction in lexA3 lysogens needed less UV than in lexA⁺ bacteria and gave 25–100% of the normal levels of infective centres induced. Assays of gene expression arising from derepression of a defective prophage showed at least 40% of the normal levels of induction by mitomycin C in lexA3 bacteria. The need for post-irradiation protein synthesis for lysogenic induction in lexA3 lysogens was reduced by increasing the basal level of recA protein with a recA⁺ plasmid. It is concluded that in lexAE. coli some recA protein synthesis, too small to be detected by physical means, is needed for UV induced lysogenic induction.