A protease inhibitor blocks SOS functions in Escherichia coli: antipain prevents lambda repressor inactivation, ultraviolet mutagenesis, and filamentous growth.

Abstract

Inhibition of DNA synthesis in E. coli by treatment with carcinogenic and mutagenic agents results in the coordinate expression of a group of diverse functions (SOS functions) including .lambda. prophage induction, filamentous growth and an error-prone DNA repair activity (SOS repair) believed to be responsible for UV mutagenesis. This SOS induction probably proceeds via irreversible proteolytic inactivation of repressor(s) for SOS functions. To test this hypothesis, the effect of a protease inhibitor, antipain [(1-carboxy-2-phenylethyl)carbamoyl-L-arginyl-L-valylargininal], on SOS induction was studied. Antipain at 0.5 mM (which has no effect on cell growth, overall RNA and protein synthesis, or induction of .beta.-galactosidase) drastically decreases mutagenesis. Antipain blocks expression of thermally induced mutator activity (another manifestation of SOS repair) and filamentous growth in a tif-1 mutant that expresses SOS functions at 42.degree. C without inhibition of DNA synthesis or detectable DNA damage. Antipain inhibits thermal induction of .lambda. prophage in the tif-1 mutant without affecting the kinetics of thermal induction of .lambda.cI857 prophage. This .lambda. mutant codes a temperature-sensitive repressor that is directly destroyed by heat and does not require the SOS induction pathway for inactivation at 42.degree. C. Apparently, antipain inhibits .lambda. prophage induction by blocking proteolytic inactivation of .lambda. repressor and inhibits the induction or expression of SOS repair and filamentous growth. A role for proteolytic cleavage in the regulation of SOS functions was suggested.