The Les- (lysogeny establishment deficient) phenotype is a pleiotropic effect of the lesB908 mutation of Pseudomonas aruginosa PAO. LesB908-containing strains are also deficient in general recombination, sensitive to UV irradiation, and deficient in UV-stimulated induction of prophages. The P. aruginosa recA-containing plasmid pKML3001 complements each of these various pleiotropic characteristics of the lesB908 mutation supporting the hypothesis that lesB908 is an allele of the P. aruginosa recA gene. The phenotypic effects of the lesB908 mutation may be best explained by the hypothesis that the lesB908 gene product is altered in such a way that it has lost synaptase activity but possesses intrinsic protease activity even in the absence of DNA damage. The Les-phenotype is a result of the rapid destruction of newly synthesized phage repressor resulting in lytic growth of the infecting virus. This hypothesis is consistent with the observations that increasing the number of copies of the phage repressor gene will also suppress the Les-phenotype in a phage-specific fashion. (Copyright (c) 1988 American Society for Microbiology.)