IDENTIFICATION AND CHARACTERIZATION OF THE CCDA GENE, REQUIRED FOR CYTOCHROME-C SYNTHESIS IN BACILLUS-SUBTILIS

The gram-positive, endospore-forming bacterium Bacillus subtilis conta ins several membrane-bound c-type cytochromes. We have isolated a muta nt pleiotropically deficient in cytochromes c. The responsible mutatio n resides in a gene which we have named ccdA (cytochrome c defective). This gene is located at 173 degrees on the B. subtilis chromosome. Th e ccdA gene was found to be specifically required for synthesis of cyt ochromes of the c type. CcdA is a predicted 26-kDa integral membrane p rotein with no clear similarity to any known cytochrome c biogenesis p rotein but seems to be related to a part of Escherichia coli DipZ/DsbD . The ccdA gene is cotranscribed with two other genes. These genes enc ode a putative 13.5-kDa single-domain response regulator, similar to B . subtilis CheY and SpoOF, and a predicted 18-kDa hydrophobic protein with no similarity to any protein in databases, respectively. Inactiva tion of the three genes showed that only ccdA is required for cytochro me c synthesis. The results also demonstrated that cytochromes of the c type are not needed for growth of B. subtilis.