Spontaneous mutagenesis is elevated in protease-defective cells.

TitleSpontaneous mutagenesis is elevated in protease-defective cells.
Publication TypeJournal Article
Year of Publication2009
AuthorsMamun, AAmar MAl, M Humayun, Z
JournalMol Microbiol
Volume71
Issue3
Pagination629-39
Date Published2009 Feb
ISSN1365-2958
KeywordsDNA Polymerase beta, DNA-Directed DNA Polymerase, Endopeptidase Clp, Escherichia coli, Escherichia coli Proteins, Frameshift Mutation, Genes, Bacterial, Mutagenesis
Abstract

As a first step towards describing the role of proteolysis in maintaining genomic integrity, we have determined the effect of the loss of ClpXP, a major energy-dependent cytoplasmic protease that degrades truncated proteins as well as a number of regulatory proteins, on spontaneous mutagenesis. In a rifampicin-sensitive to rifampicin-resistance assay that detects base substitution mutations in the essential rpoB gene, there is a modest, but appreciable increase in mutagenesis in Delta(clpP-clpX) cells relative to wild-type cells. A colony papillation analysis using a set of lacZ strains revealed that genetic -1 frameshift mutations are strongly elevated in Clp-defective cells. A quantitative analysis using a valine-sensitive to valine-resistance assay that detects frameshift mutations showed that mutagenesis is elevated 50-fold in Clp-defective cells. Elevated frameshift mutagenesis observed in Clp-deficient cells is essentially abolished in lexA1[Ind(-)] (SOS-uninducible) cells, and in cells deleted for the SOS gene dinB, which codes for DNA polymerase IV. In contrast, mutagenesis is unaffected or stimulated in cells deleted for umuC or umuD, which code for critical components of DNA polymerase V. Loss of rpoS, which codes for a stress-response sigma factor known to upregulate dinB expression in stationary phase, does not affect mutagenesis. We propose that elevated DinB expression, as well as stabilization of UmuD/UmuD' heterodimers in Delta(clpP-clpX) cells, contributes to elevated mutagenesis. These findings suggest that in normal cells, Clp-mediated proteolysis plays an important role in preventing gratuitous mutagenesis.

DOI10.1111/j.1365-2958.2008.06551.x
Alternate JournalMol. Microbiol.
PubMed ID19040636
Grant ListGM 58253 / GM / NIGMS NIH HHS / United States