Measurement of recA protein induction in Salmonella typhimurium: a possible biochemical test for the detection of DNA damaging agents.

RecA protein was purified from S. typhimurium and its concentration was measured in crude extracts by an immunoradiometric assay. The dose-response relations and the kinetics of recA protein induction following treatment of the cells with ultra-violet light, nalidixic acid, mitomycin C, and cisplatin were studied in E. coli and S. typhimurium. The recA protein amplification was complete in a few hours and was stable for at least 3 hours. Dose-response curves showed a linear region for low doses of all the inducer agents tested. This direct relation between the recA protein level and the amount of inducer agent allows the quantification of the recA protein inducing potency of chemicals. The recA protein amplification was very sensitive to low doses of inducer agents: an UV dose of 0.25 J/M2, 500 ng of NAL or 50 ng of MMC induced a two-fold increase in cellular recA protein content. In addition, the measurement of RecA protein induction did not require the survival of the cells. These observations led us to suggest a new biochemical assay for detecting DNA damaging substances by the direct measurement of the recA protein level following treatment of the cells.