In mycobacteria, as in most bacterial species, the expression of RecA is induced by DNA damage. However, the authors show here that the kinetics of induction in and in are quite different: whilst maximum expression in occurred 3–6 h after addition of a DNA-damaging agent, incubation for 18–36 h was required to reach peak levels in . This is despite the fact that the promoter can be activated more rapidly when transferred to . In addition, it is demonstrated that in both species the DNA is sufficiently damaged to give maximum induction within the first hour of incubation with mitomycin C. The difference in the induction kinetics of between the two species was mirrored by a difference in the levels of DNA-binding-competent LexA following DNA damage. A decrease in the ability of LexA to bind to the SOS box was readily detected by 2 h in , whilst a decrease was not apparent until 18–24 h in and then only a very small decrease was observed.

Keyword(s): LexA , mycobacteria and SOS induction

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