POSTTRANSCRIPTIONAL CONTROL OF A SPORULATION REGULATORY GENE ENCODING TRANSCRIPTION FACTOR-SIGMA-H IN BACILLUS-SUBTILIS

The transcriptional regulatory gene spoOH encodes an RNA polymerase sigma factor called sigma-H that directs gene expression at an early stage of sporulation in the Gram-positive bacterium Bacillus subtilis. We now report that conditions that induce sporulation cause a rapid increase in the cellular concentration of sigma-H. This increase could account for the stimulated transcription of certain sigma-H- controlled genes at the onset of sporulation. Experiments in which the expression of spoOH was monitored by use of a spoOH-lacZ fusion and in which expression of spoOH was artificially manipulated by use of an isopropyl-beta-D-thiogalactoside-inducible promoter indicate that sporulation-induced increases in the amount of sigma-H are not controlled at the level of the transcription of its structural gene. Rather, we infer the existence of post-transcriptional control mechanisms that govern sigma-H levels, and we present evidence suggesting that increases in the amount of sigma-H at the start of sporulation are due to increased translation or stability of the spoOH mRNA and, to a lesser extent, decreased turnover of spoOH protein.