An anti-sigma factor for extracytoplasmic function (ECF) sigma factor SigL. ECF sigma factors are held in an inactive form by an anti-sigma factor until released by regulated intramembrane proteolysis (RIP). 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 (Probable). Interacts with ECF RNA polymerase sigma factor SigL; this should inhibit the interaction of SigL with the RNA polymerase catalytic core. The cytosolic domain interacts with sigma factor SigL. Probably cleaved within the membrane by Rip1 near the cytoplasmic membrane interface.