INTERSPECIES REGULATION OF THE RECA GENE OF GRAM-NEGATIVE BACTERIA LACKING AN E-COLI-LIKE SOS OPERATOR

The RecA genes of Agrobacterium tumefaciens, Rhizobium meliloti, Rhizo bium phaseoli and Rhodobacter sphaeroides, species belonging to the al pha-group bacteria of the Proteobacteria class, have been fused in vit ro to the lacZ gene of Escherichia coli. By using a mini-Tn5 transposo n derivative, each of these recA-lacZ fusions was introduced into the chromosome of each of the four species, and into that of E. coli. The recA genes of three of the alpha bacteria are induced by DNA damage wh en inserted in A. tumefaciens, R. phaseoli or R. meliloti chromosomes. The expression of the recA gene of R. sphaeroides is DNA damage-media ted only when present in its own chromosome; none of the genes is indu ced in E. coli. Likewise, the recA gene of E. coli is not induced in a ny of the four alpha species. These data indicate that A. tumefaciens, R. meliloti and R. phaseoli possess a LexA-like repressor, which is a ble to block the expression of their recA genes, as well as that of R. sphaeroides, but not the recA gene of E. coli. The LexA repressor of R. sphaeroides does not repress the recA gene of A. tumefaciens, R. me liloti, R. phaseoli or E. coli.