The genes encoding both Clostridium acetobutylicum ATCC 824 butyrate synthesis pathway enzymes, phosphotransbutyrylase (ptb) and butyrate kinase (buk), were sequenced. The genes are immediately adjacent on the chromosome, with ptb preceding buk. A single transcription start point (tsp) was identified 57 bp upstream from the ptb start codon by primer extension analysis. The ptb and buk genes appear to form an operon. A putative Rho-independent terminator structure was identified 26 bp downstream from buk.