An anti-sigma factor for extracytoplasmic function (ECF) sigma factor SigK. ECF sigma factors are held in an inactive form by an anti-sigma factor until released by regulated intramembrane proteolysis (RIP). However, in M.bovis this protein is probably dysfunctional, due to at least 1 of the 2 naturally occurring polymorphisms in its gene, when compared to M.tuberculosis. This leads to an increased expression of SigK-regulated genes, such as mpb70 and mpb83. RIP occurs when an extracytoplasmic signal triggers a concerted proteolytic cascade to transmit information and elicit cellular responses. The membrane-spanning regulatory substrate protein is first cut extracytoplasmically (site-1 protease, S1P), then within the membrane itself (site-2 protease, S2P, Rip1), while cytoplasmic proteases finish degrading the regulatory protein, liberating the sigma factor (By similarity). The cytosolic domain interacts with sigma factor SigK. Belongs to the anti-sigma-K factor family.