The restriction map of a BamHI DNA fragment that contains the recA gene of Escherichia coli has been established and a large portion of the fragment's nucleotide sequence has been determined. The coding region of the recA gene contains 1059 nucleotide residues and encodes a single protein of 353 amino acid residues. The amino acid sequence of the first five residues of the NH2 terminus of the recA protein agrees with the sequence predicted from the DNA sequence except for the absence of formylmethionine in the purified protein. Immediately after the coding sequence, there is a G+C-rich sequence with dyad symmetry followed by an A+T-rich sequence. These could signal termination of transcription. The site of initiation for synthesis in vitro of the recA messenger RNA has been determined by analysis of the 5' nucleotide sequence of [gamma-32P]ATP-labeled transcripts. The promoter region shos a high degree of symmetry and contains sequences commonly found in recognition and binding sites for RNA polymerase.