Affiliation:
1. Department of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
Abstract
ABSTRACT
The RecA protein in its functional state is in complex with single-stranded DNA, i.e., in the form of a RecA filament. In SOS induction, the RecA filament functions as a coprotease, enabling the autodigestion of the LexA repressor. The RecA filament can be formed by different mechanisms, but all of them require three enzymatic activities essential for the processing of DNA double-stranded ends. These are helicase, 5′–3′ exonuclease, and RecA loading onto single-stranded DNA (ssDNA). In some mutants, the SOS response can be expressed constitutively during the process of normal DNA metabolism. The RecA730 mutant protein is able to form the RecA filament without the help of RecBCD and RecFOR mediators since it better competes with the single-strand binding (SSB) protein for ssDNA. As a consequence, the
recA730
mutants show high constitutive SOS expression. In the study described in this paper, we studied the genetic requirements for constitutive SOS expression in
recA730
mutants. Using a β-galactosidase assay, we showed that the constitutive SOS response in
recA730
mutants exhibits different requirements in different backgrounds. In a wild-type background, the constitutive SOS response is partially dependent on RecBCD function. In a
recB1080
background (the
recB1080
mutation retains only helicase), constitutive SOS expression is partially dependent on RecBCD helicase function and is strongly dependent on RecJ nuclease. Finally, in a
recB
-null background, the constitutive SOS expression of the
recA730
mutant is dependent on the RecJ nuclease. Our results emphasize the importance of the 5′–3′ exonuclease for high constitutive SOS expression in
recA730
mutants and show that RecBCD function can further enhance the excellent intrinsic abilities of the RecA730 protein
in vivo
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
8 articles.
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