Activation without Proteolysis of Anti-<i>σ</i> Factor RsiV of the Extracytoplasmic Function <i>σ</i> Factor <i>σ</i>^V in a Glucolipid-Deficient Mutant of <i>Bacillus subtilis</i>

Abstract

Extracytoplasmic function (ECF) σ factors are a crucial link in the process of bacterial response to environmental stresses, in which bacteria transmit information across the cytoplasmic membrane. Among the seven ECF σ factors of Bacillus subtilis σ V , which is sequestered by transmembrane anti- σ factor RsiV under normal growth conditions, responds to lysozyme. When B. subtilis cells are challenged by lysozyme, the lysozyme-bound RsiV undergoes two successive proteolysis steps, by a signal peptidase and RasP protease, and releases σ V . An unchallenged B. subtilis ugtP mutant lacking glucolipids exhibited higher σ V activity than wild type. However, the activation occurred in the absence of RasP, and no proteolysis of RsiV was observed. It is likely that a conformational change, not proteolysis, of RsiV leads to this activation of σ V in the absence of glucolipids. Replacement of the C-terminal region of RsiV with that of RsiW, the cognate σ factor of which, σ W , is not activated in the ugtP mutant, indicated that the C-terminal extracytoplasmic region of RsiV was necessary for the response to glucolipid deficiency.