SpoOA Pre-sporulation stage - the vegetative state of B. subtilis cells
Spo0A in the vegetative state
Transcription of the spo0A gene is regulated by two different promoters 24. The most downstream promoter (also referred to as PS) is inactive during vegetative growth and is repressed by SinR 21, by the presence of glucose 25 and by an upstream regulatory element that prevents spo0A transcription from PS during growth 26. The more upstream promoter (PV) is active during vegetative growth and is controlled by σA-bound RNA polymerase and repressed by CodY 3. The amounts of Spo0A protein produced during nutritional growth conditions 25, required for efficient entry into the state of genetic competence and for strong activation of PS at the onset of sporulation, are maintained at low levels due to a translational control mechanism 26. Due to the lack of activation through phosphorylation events and therefore the absence of key regulator responsibilities, the Spo0A protein seems to adopt a latent state – present but unable to execute its tasks. Nevertheless, its transcriptional control even at this growth stage is quite complex with a growth rate specific pulsated pattern, possibly due to fluctuations in RNA polymerase availability 5. This pulsatile expression of spo0A does not affect the transcription of stage II-specific sporulation genes and could very well function as a cell-specific preparation for responses to slow growth 5.