This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lin, L L Articles by Little, J W Search for Related Content PubMed PubMed Citation Articles by Lin, L L Articles by Little, J W

 Previous Article  |  Next Article 

J Bacteriol. 1988 May; 170(5): 2163-2173

research-article

Isolation and characterization of noncleavable (Ind-) mutants of the LexA repressor of Escherichia coli K-12.

Department of Biochemistry, University of Arizona, Tucson 85721.

ABSTRACT

The LexA repressor of Escherichia coli represses a set of genes that are expressed in the response to DNA damage. After inducing treatments, the repressor is inactivated in vivo by a specific cleavage reaction which requires an activated form of RecA protein. In vitro, specific cleavage requires activated RecA at neutral pH and proceeds spontaneously at alkaline pH. We have isolated and characterized a set of lexA mutants that are deficient in in vivo RecA-mediated cleavage but retain significant repressor function. Forty-six independent mutants, generated by hydroxylamine and formic acid mutagenesis, were isolated by a screen involving the use of operon fusions. DNA sequence analysis identified 20 different mutations. In a recA mutant, all but four of the mutant proteins functioned as repressor as well as wild-type LexA. In a strain carrying a constitutively active recA allele, recA730, all the mutant proteins repressed a sulA::lacZ fusion more efficiently than the wild-type repressor, presumably because they were cleaved poorly or not at all by the activated RecA protein. These 20 mutations resulted in amino acid substitutions in 12 positions, most of which are conserved between LexA and four other cleavable proteins. All the mutations were located in the hinge region or C-terminal domain of the protein, portions of LexA previously implicated in the specific cleavage reactions. Furthermore, these mutations were clustered in three regions, around the cleavage site (Ala-84-Gly-85) and in blocks of conserved amino acids around two residues, Ser-119 and Lys-156, which are believed essential for the cleavage reactions. These three regions of the protein thus appear to play important roles in the cleavage reaction.

This article has been cited by other articles:

• Mellies, J. L., Haack, K. R., Galligan, D. C. (2007). SOS Regulation of the Type III Secretion System of Enteropathogenic Escherichia coli. J. Bacteriol. 189: 2863-2872 [Abstract] [Full Text]  
• Sweetman, W. A., Moxon, E. R., Bayliss, C. D. (2005). Induction of the SOS regulon of Haemophilus influenzae does not affect phase variation rates at tetranucleotide or dinucleotide repeats. Microbiology 151: 2751-2763 [Abstract] [Full Text]  
• Skovgaard, O., Lobner-Olesen, A. (2005). Reduced initiation frequency from oriC restores viability of a temperature-sensitive Escherichia coli replisome mutant. Microbiology 151: 963-973 [Abstract] [Full Text]  
• Mustard, J. A., Little, J. W. (2000). Analysis of Escherichia coli RecA Interactions with LexA, lambda CI, and UmuD by Site-Directed Mutagenesis of recA. J. Bacteriol. 182: 1659-1670 [Abstract] [Full Text]  
• McLenigan, M., Peat, T. S., Frank, E. G., McDonald, J. P., Gonzalez, M., Levine, A. S., Hendrickson, W. A., Woodgate, R. (1998). Novel Escherichia coli umuD' Mutants: Structure-Function Insights into SOS Mutagenesis. J. Bacteriol. 180: 4658-4666 [Abstract] [Full Text]  
• Kuempel, P, Hogaard, A, Nielsen, M, Nagappan, O, Tecklenburg, M (1996). Use of a transposon (Tndif) to obtain suppressing and nonsuppressing insertions of the dif resolvase site of Escherichia coli.. Genes Dev. 10: 1162-1171 [Abstract]  
• McKenzie, G. J., Harris, R. S., Lee, P. L., Rosenberg, S. M. (2000). The SOS response regulates adaptive mutation. Proc. Natl. Acad. Sci. USA 97: 6646-6651 [Abstract] [Full Text]