The Bacillus subtilis sdhCAB operon contains the structural genes for the three subunits of the membrane bound succinate dehydrogenase complex. An sdh-specific transcript of about 3,450 nucleotides was detected in vegetative bacteria. S1 nuclease mapping experiments showed that the sdh operon is transcribed from a sigma-43 promoter; the transcript starts at a guanosine residue 90 base pairs upstream from the first gene of the operon, sdhC. No sdh transcript was found in B. subtilis carrying the sdh-115 mutation, which decreases expression of the sdh operon by more than 99%. The sdh-115 mutation is a G-to-A transition in the -35 region of the sigma-43 promoter. The sdh operon is sensitive to glucose repression. When the sdh promoter region was used to drive transcription of the cat-86 gene this gene also became glucose repressed.