P. mirabilis RecA protein catalyses cleavage of E. coli LexA protein and the lambda repressor in vitro.

The cloned recA+ gene of proteus mirabilis substitutes for a defective RecA protein in Escherichia coli recA- mutants, and restores recombination, repair and phage induction functions to near normal levels. In a previous report, we described the purification and characterisation of the recombination activities of the P. mirabilis RecA protein (West et al. 1983b ). In this paper, we show that the purified protein catalyses the cleavage of both the Escherichia coli LexA protein and the bacteriophage lambda repressor in vitro. These results provide a direct biochemical basis for the interspecies complementation observed in vivo and suggest that P. mirabilis has an SOS regulatory network similar to that of E. coli.