Prophage phi 80 is induced in Escherichia coli K12 recA430

In contrast to prophage lambda, wild-type prophage phi 80 was induced by UV-irradiation or thymine deprivation in recA430 mutants of E. coli K12. There was no induction of prophage phi 80 in two recombination-deficient mutants recA13 and recA99. Phage phi 80ind3, a non-inducible derivative in a rec+ was not induced in a recA430 lysogen. Two other lambdoid prophages were tested for UV-induction in recA430 lysogens: in common with lambda prophage, 434 was not induced whereas prophage 21 was induced in 1% of the cells. Induction of RecA430 protein synthesis was 30% of that observed in recA+ bacteria at 30 min of post-irradiation incubation, indicating that LexA repressor had been cleaved by RecA430 protease. In lexA1 recA430 and lexA1 recA+ bacteria, RecA protein synthesis was not amplified, yet, prophage phi 80 was fully induced. If phi 80cI repressor is inactivated by cleavage by RecA430 protease as is LexA repressor, RecA430 protease can inactivate all the molecules of phi 80cI repressor, its basal level being high enough in a recA430 lysogen. In such a lysogen, a fraction only of 21cI and LexA repressors are cleaved but no molecules of either lambda cI or 434cI repressor. We postulate that RecA430 protein has an altered pattern of recognition of repressor molecules and a cleavage efficiency which is more efficient the more remote is the repressor conformation from that of lambda repressor.