Genetic characterization of the inducible SOS-like system of Bacillus subtilis

The SOS-like system of Bacillus subtilis consists of several coordinately induced phenomena (e.g., cellular filamentation, prophage induction, and Weigle reactivation of UV-damaged bacteriophage) which are expressed after cellular insult such as DNA damage or inhibition of DNA replication. Mutagenesis of the bacterial chromosome and the development or maintenance of competence also appear to be involved in the SOS-like response in this bacterium. The genetic characterization of the SOS-like system has involved an analysis of (i) the effects of various DNA repair mutations on the expression of inducible phenomena and (ii) the tsi-23 mutation, which renders host strains thermally inducible for each of the SOS-like functions. Bacterial filamentation was unaffected by any of the DNA repair mutations studied. In contrast, the induction of prophage after thermal or UV pretreatment was abolished in strains carrying the recE4, recA1, recB2, or recG13 mutation. The Weigle reactivation of UV-damaged bacteriophage was also inhibited by the recE4, recA1, recB2, or recG13 mutation, whereas levels of Weigle reactivation were lower in strains which carried the uvrA42, polA5, or rec-961 mutation than in the DNA repair-proficient strain. Strains which carried the recE4 mutation were incapable of chromosomal DNA-mediated transformation, and the frequency of this event was decreased in strains carrying the recA1, recB2, or tsi-23 mutation. Plasmid DNA transformation efficiency was decreased only in strains carrying the tsi-23 mutation in addition to the recE4, recA1, or recB2 mutation. The results indicate that the SOS-like system of B. subtilis is regulated at different levels by two or more gene products. In this report, the current data regarding the genetic regulation of inducible phenomena are summarized, and a model is proposed to explain the mechanism of SOS-like induction in B. subtilis.