Nucleotide sequence and LexA regulation of the Escherichia coli recS gene

The nucleotide sequence of a 2224 bp region of the Escherichia co l i chromosome that c a r r i e s the LexA regulated recN gene has been determined. A region of 1701 nucleot ides encoding a polypeptide of 567 amino acids with a predicted molecular weight of 63,599 was iden t i f i ed as the most probable sequence for the recN s t r u c t u r a l gene. The proposed i n i t i a t i o n codon i s preceded by a reasonable Shine-Dalgarno sequence and a promoter region containing two 16 bp sequences, separated by 6 bp, that match the consensus sequence (SOS box) for binding LexA protein . DNA fragments containing t h i s putat ive promoter region are shown to bind LexA in v i t r o and to have LexA-regula ted promoter a c t i v i t y ^ n v i v o . The amino ac id sequence of RecN predicted from the DNA contains a region tha t i s homologous to highly conserved sequences found in several DNA repa i r enzymes and other proteins tha t bind ATP. A sequence of 9 amino acids was found to be homologous to a region of the RecA protein of E^ co l i postulated to have a ro le in DNA/nucleotide binding.