NORMAL INDUCTION OF THE SOS RESPONSE IN BACILLUS-SUBTILIS IS PREVENTED BY THE MUTANT REPRESSOR FROM PHAGE PHI-105CTS23

The presence of the Phi 105cts23 mutant prophage in Bacillus subtilis induces a series of pleiotropic effects that could be ascribed to an a nti-SOS activity. In order to circumvent the phage function responsibl e for this phenomenon, the cts23 mutant repressor was cloned and seque nced. The isolated repressor reduced the survival capacity of the host cells after mitomycin C or nalidixic acid treatments and lowered the spontaneous reversion frequency. When SOS induction kinetics were stud ied, low or null induction of the damage-inducible din22::LacZ fusion was observed. In contrast, the presence of the wild-type prophage ampl ified the SOS response. Sequencing of the mutant repressor revealed th at the cts23 mutation is a T --> C transition affecting the 5' closest codon to one of the two reported DNA binding domains. (C) 1998 Federa tion of European Microbiological Societies. Published by Elsevier Scie nce B.V. All rights reserved.