Induction of σB-dependent general stress genes by amino acid starvation in a spo0H mutant of Bacillus subtilis

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Abstract
Solely σB-dependent genes like gsiB and gspA are not significantly induced in amino acid-starved wild-type cells, since amino acid starvation does not trigger activation of σB. The general stress gene yvyD is subject to the control of both σB and σH therefore displaying induction in response to amino acid starvation at the σH-dependent promoter. Surprisingly, the proteins YvyD, GsiB and GspA were significantly induced in amino acid-starved cells of a strain lacking σH activity. Transcriptional studies provided evidence that σB-dependent transcription is indeed induced in a spo0H mutant during amino acid starvation and depends on RsbP but not on RsbU indicating that the stress signal transduction is not required for this induction. A similar phenomenon of σB activation was observed in amino acid-starved cells of a spo0A deletion mutant. The σB-dependent transcription in a spo0H mutant further needs an active RelA protein which is responsible for strong repression of house-keeping genes after amino acid starvation (stringent response). Our data indicate that in the absence of σH and under conditions which provoke the stringent response, RsbP-dependent levels of active σB can more effectively compete for increased levels of free RNA polymerase core enzyme leading to the induction of the probably strongest σB-dependent genes.