THE EXPRESSION OF THE ACINETOBACTER-CALCOACETICUS RECA GENE INCREASESIN RESPONSE TO DNA-DAMAGE INDEPENDENTLY OF RECA AND OF DEVELOPMENT OFCOMPETENCE FOR NATURAL TRANSFORMATION

Using the lacZ operon fusion technique, the transcriptional control of the Acinetobacter calcoaceticus recA gene was studied. A low (approxi mately twofold) inductive capacity was observed for compounds that dam age DMA and/or inhibit DNA replication, e.g. methyl methanesulfonate, mitomycin C, UV light and nalidixic acid. Induction of the recA gene b y DNA damage was independent of functional RecA. The presence of the r ecA promoter region on a multicopy plasmid had the same effect on recA transcription as the presence of DNA-damaging agents. Thus, recA expr ession in A. calcoaceticus appears to be regulated in a novel fashion, possibly involving a non-LexA-like repressor. Regulation of the recA gene in A. calcoaceticus appears not to be part of a regulon responsib le for competence for natural transformation: in cells exhibiting extr emely low transformation frequencies, the level of transcription of th e recA gene was found to be comparable to the level found in cells in the state of maximal competence.