The Activity of σV, an Extracytoplasmic Function σ Factor of Bacillus subtilis, Is Controlled by Regulated Proteolysis of the Anti-σ Factor RsiV

During growth in the environment, bacteria encounter stresses which can delay or inhibit their growth. To defend against these stresses, bacteria induce both resistance and repair mechanisms. Many bacteria regulate these resistance mechanisms using a group of alternative sigma factors called extracytoplasmic function (ECF) sigma factors. ECF sigma factors represent the largest and most diverse family of sigma factors. Here, we demonstrate that the activation of a member of the ECF30 subfamily of ECF sigma factors, sigma(V) in Bacillus subtilis, is controlled by the proteolytic destruction of the anti-sigma factor RsiV. We will demonstrate that the degradation of RsiV and, thus, the activation of sigma(V) requires multiple proteolytic steps. Upon exposure to the inducer lysozyme, the extracellular domain of RsiV is removed by an unknown protease, which cleaves at site 1. This cleavage is independent of PrsW, the B. subtilis site 1 protease, which cleaves the anti-sigma factor RsiW. Following cleavage by the unknown protease, the N-terminal portion of RsiV requires further processing, which requires the site 2 intramembrane protease RasP. Our data indicate that the N-terminal portion of RsiV from amino acid 1 to 60, which lacks the extracellular domain, is constitutively degraded unless RasP is absent, indicating that RasP cleavage is constitutive. This suggests that the regulatory step in RsiV degradation and, thus, sigma(V) activation are controlled at the level of the site 1 cleavage. Finally, we provide evidence that increased resistance to lysozyme decreases sigma(V) activation. Collectively, these data provide evidence that the mechanism for sigma(V) activation in B. subtilis is controlled by regulated intramembrane proteolysis (RIP) and requires the site 2 protease RasP.