The nucleotide sequence of a 2.7-kb region of Clostridium acetobutylicum ATCC 824 DNA containing three open reading frames was determined. They encoded homologs of three proteins of Bacillus subtilis, and the gene arrangement in both organisms was identical. The first gene, orfA, was 801-bp long; the 31-kDa (266 aa) product it encoded exhibited homology with the putative sigma E-processing enzyme. The second gene, sigE, was 708-bp long encoding a 27-kDa (235 aa) product; the third gene, sigG, was 774-bp long encoding a 30-kDa (257 aa) product. These two proteins showed high homology with sigma E and sigma G, two sporulation-specific sigma factors.