An anti-sigma factor antagonist is an anti-anti-sigma factor, which relieves inhibition of sigma factor activity by the anti-sigma factor. Examples include the <taxon tax_id="1423">Bacillus subtilis</taxon> SpoIIAA protein, which, in its phosphorylated form, acts as an anti-anti-sigma factor to relieve SpoIIAB inhibition of sigma F; and the anti-sigma B factor antagonist, RsbV, which counteracts the RsbW-mediated inhibition of sigma B by binding to RsbW.