Self-reinforcing activation of a cell-specific transcription factor by proteolysis of an anti-σ factor in B-subtilis

The transcription factor sigma (F), which is activated in a cell-specific manner during sporulation in B. subtilis, is initially held in an inactive complex by the anti-sigma factor SpollAB. The anti-anti-sigma factor SpollAA reacts with SpollAB(.)sigma (F) to induce the release of free sigma (F) and free SpollAB. We now report that free SpollAB is subject to proteolysis and that it is protected from degradation by sigma (F) in the SpollAB(.)sigma (F) complex and by SpollAA in an alternative complex. Proteolysis requires residues located near the extreme C terminus of SpollAB and is dependent upon the ClpCP protease. The reaction of SpollAA with SpollAB(.)sigma (F) and the resulting degradation of newly released SpollAB could set up a self-reinforcing cycle that locks on the activation of sigma (F).