The sigma (σ) subunit of prokaryotic RNA polymerase

Sigma (σ) factor recognizes promotor sequences on the DNA template. Different factors recognize a different group of genes. α-amanitin inhibit RNA polymerase II of eukaryotes. Rifampicin inhibits β-subunit of RNA polymerase. Sigma unit is not a part of core enzyme; it is a part of holoenzyme. RNA polymerase (holoenzyme) = core enzyme (2α, β,( β’) + sigma (σ) subunit