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J. Bacteriol., Mar 1997, 1698-1703, Vol 179, No. 5
KW Winterling, AS Levine, RE Yasbin and R Woodgate
In Bacillus subtilis, exposure to DNA damage and the development of natural
competence lead to the induction of the SOS regulon. It has been
hypothesized that the DinR protein is the cellular repressor of the B.
subtilis SOS system due to its homology to the Escherichia coli LexA
transcriptional repressor. Indeed, comparison of DinR and its homologs from
gram-negative and -positive bacteria revealed conserved structural motifs
within the carboxyl-terminal domain that are believed to be important for
autocatalysis of the protein. In contrast, regions within the DNA binding
domain were conserved only within gram-negative or -positive genera, which
possibly explains the differences in the sequence specificities between
gram-negative and gram-positive SOS boxes. The hypothesis that DinR is the
repressor of the SOS regulon in B. subtilis has been tested through
overexpression, purification, and characterization of the DinR protein.
Like E. coli LexA, B. subtilis DinR undergoes an autocatalytic reaction at
alkaline pH at a siscile Ala91-Gly92 bond. The cleavage reaction can also
be mediated in vitro under more physiological conditions by the E. coli
RecA protein. By using electrophoretic mobility shift assays, we
demonstrated that DinR interacts with the previously characterized SOS box
of the B. subtilis recA gene, but not with sequences containing single base
pair mutations within the SOS box. Together, these observations strongly
suggest that DinR is the repressor of the SOS regulon in B. subtilis.
Copyright © 1997, American Society for Microbiology
Characterization of DinR, the Bacillus subtilis SOS repressor
Section on DNA replication, repair, and mutagenesis, National Institute of Child Health and Human Development, Bethesda, Maryland 20892-2725, USA.
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