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Characterization of the SOS Regulon of Caulobacter crescentus ^,

Raquel Paes da Rocha, Apuã César de Miranda Paquola, Marilis do Valle Marques, Carlos Frederico Martins Menck,^* and Rodrigo S. Galhardo

Department of Microbiology, Institute of Biomedical Sciences, São Paulo University, São Paulo, Brazil

Received 31 August 2007/ Accepted 5 December 2007

The SOS regulon is a paradigm of bacterial responses to DNA damage. A wide variety of bacterial species possess homologs of lexA and recA, the central players in the regulation of the SOS circuit. Nevertheless, the genes actually regulated by the SOS have been determined only experimentally in a few bacterial species. In this work, we describe 37 genes regulated in a LexA-dependent manner in the alphaproteobacterium Caulobacter crescentus. In agreement with previous results, we have found that the direct repeat GTTCN₇GTTC is the SOS operator of C. crescentus, which was confirmed by site-directed mutagenesis studies of the imuA promoter. Several potential promoter regions containing the SOS operator were identified in the genome, and the expression of the corresponding genes was analyzed for both the wild type and the lexA strain, demonstrating that the vast majority of these genes are indeed SOS regulated. Interestingly, many of these genes encode proteins with unknown functions, revealing the potential of this approach for the discovery of novel genes involved in cellular responses to DNA damage in prokaryotes, and illustrating the diversity of SOS-regulated genes among different bacterial species.

Published ahead of print on 14 December 2007.

Supplemental material for this article may be found at http://jb.asm.org/.

Present address: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX.