The regulation of the fumarase (citG) gene of Bacillus subtilis 168.

The level of fumarase activity in Bacillus subtilis depends on the nutritional environment; in rich medium low vegetative levels increase towards the end of the exponential phase, whereas in minimal glucose medium levels are relatively high throughout growth. Analysis of the enzyme levels in spoO mutants has revealed that a functional spoOH gene is required for the efficient expression of fumarase in both media. This highlights a regulatory role for the spoOH gene product not only in control of postexponentially expressed genes, but also during vegetative growth in defined medium. S1 transcript mapping reveals three transcriptional startpoints for the fumarase structural gene (citG) in B. subtilis. The upstream promoter region P1, which appears to contain two transcriptional startpoints, is functional in both Escherichia coli and B. subtilis. Promoter P2, which is located closer to the structural gene, is only functional in B. subtilis. Transcription from this promoter is strictly dependent on a functional spoOH gene; this gene has recently been shown to encode a minor sigma factor.