The NfrA protein, an oxidoreductase from the soil bacterium Bacillus subtilis, is synthesized during the stationary phase and in response to heat. Analysis of promoter mutants revealed that the nfrA gene belongs to the class III heat shock genes in B. subtilis. An approximate 10-fold induction at both the transcriptional and the translational levels was found after thermal upshock. This induction resulted from enhanced synthesis of mRNA. Genetic and Northern blot analyses revealed that nfrA and the gene downstream of nfrA are transcribed as a bicistronic transcriptional unit. The unstable full-length transcript is processed into two short transcripts encoding nfrA and ywcH. The nfrA-ywcH operon is not induced by salt stress or by ethanol. According to previously published data, the transcription of class III genes in general is activated in response to the addition of these stressors. However, this conclusion is based on experiments which lacked a valid control. Therefore, it seems possible that the transcription of all class III genes is specifically induced by heat shock.The continuous demand of Bacillus subtilis to adapt to everchanging conditions in its natural environment has forced the generation of complex regulatory mechanisms governing the transcription of stress-specific proteins. Stress-inducible genes from B. subtilis in general are subdivided into three groups (17,18). Class I genes are specifically induced by heat stress (17). The well-known chaperonins GroEL, GroES, DnaK, DnaJ, and GrpE are encoded by genes belonging to this group (30,41,48,54,55). The transcription of the respective genes is regulated by HrcA, a transcription repressor which binds to the CIRCE element (43,56,57,59). Genes transcribed in a Bdependent manner constitute class II stress-responsive genes (17, 18). B activity is triggered by different kinds of stress and by starvation (5, 7-9). Members of the last group of stressinduced genes, class III, are induced not by starvation but by several different stressful conditions. The transcription of class III genes is neither repressed by HrcA nor solely dependent on B . The regulator of the clpC operon, which encodes class III proteins, is known (11,27). This operon is transcribed by the activity of RNA polymerases containing B and A (28). Nevertheless, transcription is not induced at the onset of the stationary phase (28), likely because of the activity of this regulator (11,27).Some of the stress-responsive proteins are regulated by two transcription factors. clpC, dps, trxA, opuE, and clpP (1,4,15,29,40,46) are transcribed by RNA polymerase containing either A or B . csbB is under the additional control of X (22). The csb40 operon (50) and the yvyD gene (13) are transcribed from B and H promoters, respectively. This genetic organization enables the bacterial cell to modulate the regulation of the respective genes in response to additional challenges.In this communication, we describe the transcriptional regulation of the nfrA-ywcH operon encoding an oxidoreductase (34, 58) and a p...

SummaryWe investigated the function and transcriptional regulation of ywcG. The protein is essential for Bacillus subtilis. Biochemical characterization of the protein revealed that it is an FMN-containing NADPH oxidase. ywcG is transcribed throughout the whole life cycle of B. subtilis. The start point of transcription is preceded by potential promoter sequences for A , B and D . A boost in transcription occurs at the beginning of stationary phase in complex media containing glutamate and glucose. The induction of transcription at the beginning of stationary phase needs the activity of a different alternative -factor D . ywcG is, therefore, the first gene with a putative role in energy metabolism from B. subtilis that is transcribed in a D -dependent fashion, but its regulation is unique and the reverse of that described for all other D -dependent genes.