Suppression of induction of SOS functions in an Escherichia coli tif-1 mutant by plasmid R100.1.

The tif-1 mutation in the recA gene of Escherichia coli caused, at 40 degrees C, lethal cell filamentation, induction of the recA protein, mutagenesis, and, in lambda lysogens, prophage induction. The presence of plasmid R100.1 in tif-1 strains suppressed tif-mediated cell filamentation and killing, recA protein induction, and prophage induction in lysogens. It also reduced mutagenesis in a tif-1 sfiA11(R100.1) strain. Plasmids F'lac, P1, and pMB9, in contrast, had little or no effect on tif-mediated induction of lambda. The presence of R100.1 did not inhibit the induction of the recA protein or of lambda by ultraviolet irradiation or mitomycin C treatment of tif-1(R100.1) or tif-1(lambda)(R100.1) strains.