SporeWeb

SigH Starvation – activation of Spo0A

SigH during starvation

The increased levels of Spo0A~P in stationary phase cells lift the repression on the spo0H gene through the inactivation of AbrB. This leads to increased spo0H transcription that, in conjunction with posttranscriptional stabilization ⁵⁹, causes accumulation of σ^H levels and induced transcription of the σ^H regulon ⁶⁰, including the spo0A, kinA, spo0F and spoIIA genes ⁶¹. The subsequent increased production of KinA, Spo0F and Spo0A results in a rapid rise of phosphorylated Spo0A, which establishes a positive feedback loop ⁶² required for the production of Spo0A~P protein to exceed high threshold levels needed to start the sporulation process ⁴³. In adaptation to nutrient depletion conditions, ever-changing external factors influence the regulation of σ^H even further on different levels, which is reflected also by its regulatory effect on genes involved ⁶³.