How sigma docks to RNA polymerase and what sigma does

It is clear that multiple sites of interaction exist between sigmas and cor e subunits, likely reflecting the changing pattern of interactions that occ ur sequentially during the complex process of holoenzyme formation, open pr omoter formation, and initiation of transcription. Recent studies have reve aled that a major site of interaction of Escherichia coli sigma factors is the amino acid 260-309 coiled-coil region of the beta ' subunit of core RNA polymerase. This region of beta ' interacts with region 2.1-2.2 of sigma ( 70), Binding of this region of beta ' to sigma (70) triggers a conformation al change in sigma that allows it to bind to a -10 nontemplate promoter DNA strand oligonucleotide.