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 σH levels and induced transcription of the σH 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 σH even further on different levels, which is reflected also by its regulatory effect on genes involved 63.