The sigma (s) subunit of prokaryotic RNA polymerase
High-Yield Explanation
prokaryotic RNA polymers contain 2 alpha subunit, 2 beta subunit, 1 omega subunit, 1 sigma subunit and 2 zinc molecules Beta subunit fixes at the initiation siteThe sigma factor recognizes the promoter site and the affinity of the holoenzyme to the promoter siteRef: DM Vasudevan, 7th edition, page no: 589