The sacU locus has been cloned by using two independent strategies, and the presence of two open reading frames was deduced from the nucleotide sequence. Open reading frame 1 encodes a 45,000-dalton polypeptide that is similar to the products of the Salmonella typhimurium cheA and Escherichia coli cpxA genes, which act as sensory transducers. Open reading frame 2 encodes a 26,000-dalton polypeptide that is similar to a family of transcriptional activators, including the products of the Bacillus subtilis spoOA and spoOF and the E. coli ompR and dye genes. These similarities suggest that the products of the B. subtilis sacU locus form a sensor-transducer couple, which functions to relay information about specific environmental changes to the transcription apparatus.