Induction by mitomycin C of recA protein synthesis in bacteria and spheroplasts

The effect of mitomycin C on the synthesis of recA protein in Escherichia coli has been analyzed in a variety of conditions, using an immunoradiometric assay (Paoletti, C., Salles, B., and Giacomoni, P. U. (1982) Biochimie 64, 239-246). In exponentially growing cultures of E. coli AB 1157, the addition of mitomycin C (5 micrograms/ml) promotes a 15-fold increase of the content of recA protein with respect to the basal level. Kinetic analysis of this induction shows that the maximum is reached 60 to 90 min after the addition of the drug and then the level decreases. In an uvrA mutant treated with mitomycin C the level of recA protein reaches a maximum within an hour and afterwards it does not decrease. Treatment of exponentially growing cells with EDTA and lysozyme induces a 3-fold increase of recA protein content, in comparison to the basal level. When such spheroplasts are added with mitomycin or nalidixic acid, a striking increase of the recA protein content in the spheroplast suspension is observed, which tends to level off an hour and a half after the addition of the drugs. The maximum level of recA protein content is five times the level measured after lysozyme treatment, i.e. 15 times the basal level in exponentially growing cells.