A 2,695 bp chromosomal segment of Escherichia coli K12 containing the recQ gene was sequenced. Analysis of the sequence revealed an open reading frame thought to represent recQ, with a clockwise direction of transcription relative to the standard genetic map of E. coli K12 and having a coding capacity for a protein of Mr 68,350. The -10 region of the presumptive recQ promoter overlapped the putative terminator for the upstream gene pldA, and was immediately followed by a 15 bp stretch of DNA bearing a strong resemblance to the reported sequences of LexA repressor binding sites. This latter finding suggested the possibility of SOS regulation of recQ gene expression, which was substantiated by experiments with recQ-lacZ fusions.