1887

Abstract

LexA protein is the repressor of a gene network whose members are directly involved in the repair of damaged DNA and in the survival of bacterial cells until DNA lesions have been eliminated. The gene is widely present in bacteria, although the sequences of only three LexA-binding sites are known: Gram-positive, alpha and some members of gamma represented by . Taking advantage of the fact that the genome sequence of the plant-pathogenic bacterium has been determined, its gene has been cloned and overexpressed in to purify its product. After demonstration that and genes are co-transcribed, gel mobility shift assays and directed mutagenesis experiments using the promoter of the transcriptional unit demonstrated that the LexA protein specifically binds the imperfect palindrome TTAGNTACTA. This is the first LexA binding sequence identified in the gamma differing from the -like LexA box. Although a computational search has revealed the presence of TTAGNTACTA-like motifs upstream of genes other than , LexA only binds the promoter of one of them, XF2313, encoding a putative DNA-modification methylase. Moreover, LexA protein does not bind any of the other genes whose homologues are regulated by the LexA repressor in (, , , , , , and ). RT-PCR quantitative analysis has also demonstrated that and XF2313 genes, as well as the genes which are homologues to those of belonging to the LexA regulon, with the exception of , are DNA damage-inducible in .

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2002-11-01
2020-09-26
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