Expression of Primary Sigma Factor (PSF) and PSF-Like Sigma Factors in the Cyanobacterium Synechocystis sp. Strain PCC 6803

Large amounts of sigA mRNA, encoding the primary σ factor (PSF) in Synechocystis sp. strain PCC 6803, accumulated under standard growth conditions, while stress conditions like heat or high salinity led to a rapid decrease in sigA mRNA content. The sigB, sigC, sigD, and sigE genes, encoding PSF-like σ factors, were under strict physiological control.