A SIGMA(E)-DEPENDENT OPERON SUBJECT TO CATABOLITE REPRESSION DURING SPORULATION IN BACILLUS-SUBTILIS

To identify genes expressed at intermediate stages of Bacillus subtili s sporulation, we screened for sigma(E)-dependent promoters. One promo tes that we found drives expression of an operon consisting of at leas t five open reading frames (ORFs). The predicted products of the first three ORFs are very homologous to enzymes involved in fatty acid meta bolism, including acetyl coenzyme A (acetyl-CoA) acetyltransferase (th iolase), 3-hydroxybutyryl-CoA dehydrogenase, and acyl-CoA dehydrogenas e, respectively. We showed that the Fourth ORF encoded a third isozyme of citrate synthase in B. subtilis. Genetic evidence and primer exten sion results showed that transcription of this operon is directed by t he mother cell compartment-specific sigma factor, sigma(E) and so the operon was named mmg (for mother cell metabolic genes). Furthermore, w e found that a sequence (mmgO) with homology to a catabolite-responsiv e element mediates glucose repression of mmg promoter activity during sporulation and that this repression was lost in a ccpA mutant.