A protease inhibitor blocks SOS functions in Escherichia coli: antipain prevents λ 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 coorinate expression of a group of diverse functions(SOS functions) including λ prophage induction, filamentous growth, and an error prone DNA repair activity (SOS repair) believed to be responsible for ultraviolet mutagenesis. It has been proposed that this SOS induction proceeds via irreversible proteolytic inactivation of repressor(s) for SOS functions. To test this hypothesis, we investigated the effect of a protaase inhibitor, antipain [(1-carboxy-2-phenylethyl) carbamoyl-L-arginyl-L-valylargininal], on SOS induction. We found that 0.5 mM antipain (which has no effect on cell growth, overall RNA and protein synthesis, or induction of β galactosidase) drastically decreases mutagenesis. Antipain also blocks of thermally induced mutator activity (another manifestation of SOS repair) and filamentous growth in a tif-1 mutant that expresses SOS functions at 40°C without inhibition of DNA synthesis or detectable DNA damage. Furthermore, antipain inhibits thermal induction of λ prophage in the tif-1 mutant withou affecting the kinetics of thermal induction of λc1857 prophage. This λ mutant codes a temperature sensitivity repressor that is directly destroyed by heat and does not require the SOS induction pathway for inactivation at 42°. From our results we conclude that antipain inhibits λ prophage induction by blocking proteolytic inactivation of λ repressor and that it inhibits the induction or expression of SOS repair and filamentous growth. Our resuls suggested a role for proteolytic cleavage in the regulation of SOS functions.