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. 1991 Aug 15;88(16):7356–7360. doi: 10.1073/pnas.88.16.7356

Mutant LexA proteins with an increased rate of in vivo cleavage.

M H Smith 1, M M Cavenagh 1, J W Little 1
PMCID: PMC52294  PMID: 1908093

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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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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