The RNA polymerase sigma factor afH is essential for the onset of endospore formation in Bacillus subtilis.rH also is required for several additional stationary-phase-specific responses, including the normal expression of several genes that are required for the development of competence for DNA uptake. It is necessary to identify the genes that are transcribed by (rH RNA polymerase (EiH) in order to understand the role of this sigma factor during the transition from exponential growth to stationary phase. Feavers et al. (Mol. Gen. Genet. 211:465-471, 1988) proposed that MIG, the structural gene for fumarase, is transcribed from two promoters, one of which (citGp2 [P2]) may be used by EYH. It is likely that the citGp2 promoter is used by ErH because we found that this promoter was used accurately in vitro by EifH and directed expression of xylE in vivo. This xylE expression was dependent on spoOH, the structural gene for CfH, and was independent of the citGpl promoter. Comparison of the nucleotide sequences of several CfH-dependent promoters showed that these sequences were similar at two regions approximately 10 and 35 base pairs upstream from the start points of transcription. These sequences may signal recognition of these promoters by ECfH. Primer extension analyses were used to examine transcription from three fH-dependent promoters during growth and sporulation. The citGp2 promoter appeared to be active during the middle and late stages of exponential growth, whereas activation of the spoIIA promoter was delayed until after the end of exponential growth. Evidently, promoters used by EiH can display different temporal patterns of expression.Sigma H (uH) is one of at least nine different RNA polymerase sigma factors produced by the bacterium Bacillus subtilis (14, 15). Association of each sigma factor with the core subunits of RNA polymerase directs the holoenzyme to use a different class of transcriptional promoters. Since mutations in spoOH, the structural gene for aH (6), prevent the onset of sporulation, it is likely that RNA polymerase containing (7H (ECH) transcribes at least one gene that is necessary for the onset of sporulation. Mutations in spoOH also reduce the development of competence for DNA uptake (1) and the production of stationary-phase-specific extracellular enzymes (8). Evidently, EuH transcribes a diverse group of genes that play important roles in the bacterium's responses to nutrient depletion.The genes that are transcribed by EuH and necessary for the stationary-phase-specific responses are unknown. EuH has been shown to use two promoters, spoVG (22) and rpoDp3 (4), but transcription from these two promoters is not necessary for the onset of sporulation or the other stationary-phase-specific responses (18; R. H. Doi, personal communication). Moreover, recent results show that crA, the primary sigma factor in growing cells, directs the transcription of several sporulation-essential genes at the onset of endospore formation (9, 11; T. J. Kenney, K. York, P. Youngman, and C. P. Moran, J...

Transcription of the etc gene in Bacillus subtilis is activated only after exponentially growing cells enter stationary phase. The promoter of the ctc gene is utilized in vitro by two minor forms of RNA polymerase, Ec37 and Eu32, but not by the most abundant form of RNA polymerase, Er-55. We have used the ctc promoter to direct transcription of the xylE gene on plasmid pLC4 and observed that xylE was expressed only in stationary-phase B. subtilis. We also have constructed a series of homologous plasmids that differ only by