An anti-sigma factor for extracytoplasmic function (ECF) sigma factor SigE. ECF sigma factors are held in an inactive form by an anti-sigma factor. Binds 1 Zn(2+) ion per subunit. Interacts with cognate ECF RNA polymerase sigma factor SigE under reducing conditions; this inhibits the interaction of SigE with the RNA polymerase catalytic core. Phosphorylated by PknB on Thr-39; can be dephosphorylated (at least in vitro) by PstP. Phosphorylation is the signal for subsequent degradation by the ClpC1-ClpP2 complex. Degraded following vancomycin treatment (surface stress) by a ClpC1-ClpP2 complex. Belongs to the zinc-associated anti-sigma factor (ZAS) superfamily. Extended N-terminus.