Affiliation:
1. Department of Molecular Biology, Faculty of Science, University of Zagreb
2. Department of Molecular Biology, Ruðer Bošković Institute, Zagreb, Croatia
Abstract
ABSTRACT
The SOS response in
Escherichia coli
results in the coordinately induced expression of more than 40 genes which occurs when cells are treated with DNA-damaging agents. This response is dependent on RecA (coprotease), LexA (repressor), and the presence of single-stranded DNA (ssDNA). A prerequisite for SOS induction is the formation of a RecA-ssDNA filament. Depending on the DNA substrate, the RecA-ssDNA filament is produced by either RecBCD, RecFOR, or a hybrid recombination mechansim with specific enzyme activities, including helicase, exonuclease, and RecA loading. In this study we examined the role of RecA loading activity in SOS induction after UV irradiation. We performed a genetic analysis of SOS induction in strains with a mutation which eliminates RecA loading activity in the RecBCD enzyme (
recB1080
allele). We found that RecA loading activity is essential for SOS induction. In the
recB1080
mutant RecQ helicase is not important, whereas RecJ nuclease slightly decreases SOS induction after UV irradiation. In addition, we found that the
recB1080
mutant exhibited constitutive expression of the SOS regulon. Surprisingly, this constitutive SOS expression was dependent on the RecJ protein but not on RecFOR, implying that there is a different mechanism of RecA loading for constitutive SOS expression.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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