Mutant LexA Proteins with an Increased Rate of in Vivo Cleavage

Overview

Journal Proc Natl Acad Sci U S A

Specialty Science

Date 1991 Aug 15

PMID 1908093

Citations 13

Authors

M H Smith

M M Cavenagh

J W Little

Affiliations

Soon will be listed here.

Abstract

LexA repressor of Escherichia coli is inactivated by a specific cleavage reaction that requires activated RecA protein in vivo. This cleavage reaction can proceed in vitro in the presence of activated RecA or as an intramolecular RecA-independent reaction, termed autodigestion, that is stimulated by alkaline pH. Here we describe a set of LexA mutant proteins that undergo a greatly increased rate of specific cleavage in vivo, compared with wild-type LexA. Efficient in vivo cleavage of these mutant proteins also took place without RecA. Several lines of evidence suggest that cleavage occurred via a mechanism similar to autodigestion. These mutations changed Gln-92, which lies near the cleavage site, to tyrosine, phenylalanine, or tryptophan. The latter mutation increased the rate of cleavage approximately 500-fold. These findings imply that the rate of wild-type LexA cleavage has been optimized during evolution to make the SOS system properly responsive to DNA-damaging treatments. Availability of these mutants will aid in the understanding of rate-limiting steps in intramolecular reactions.

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