The Escherichia coli K-12 trxA gene, the gene encoding thioredoxin, has been cloned and sequenced. The DNA sequence includes 280 base pairs upstream and 46 base pairs downstream of the coding region. The downstream sequence contains the -35 region of the promoter of the rho gene. Northern analysis of the trxA mRNA and S1 nuclease mapping indicate the presence of two promoters for the trxA gene. Initiation from either promoter results in an mRNA containing two potential translation initiation codons, one of which could initiate synthesis of a protein 18 amino acids longer than the mature trxA gene product. The 3' end of the gene, including the last eight codons, contains a stable stem-loop structure (delta G = -12.9 kcal) typical of a rho-independent transcription termination signal.