The activity of σV, an extracytoplasmic function σ factor of Bacillus subtilis, is controlled by regulated proteolysis of the anti-σ factor RsiV.
Extracytoplasmic function (ECF) σ factors respond to environmental stresses and regulate numerous genes required for adaptation. Under normal growth conditions, the ECF σ factors are sequestered by transmembrane anti-σ factor proteins, from which they are released under stress conditions. In Bacillus subtilis ugtP null mutant cells, which lack glucolipids, three of the seven ECF σ factors, σM, σV and σX, are activated. The Escherichia coli cell membrane does not contain glucolipids. When the genes for these three ECF σ and anti-σ factors were introduced into E. coli cells, expression of lacZ fused to the ECF σ factor-regulated promoters indicated ECF σ factor activity. Additional expression of the ugtP gene in these E. coli cells led to the synthesis of small amounts of glucolipids, and the activities of σM and σV were repressed, but the activity of σX was unaffected. It is likely that glucolipids directly influence anti-σM and anti-σV factors by stabilizing conformations that sequester the respective ECF σ factors.