Identification of RNA polymerase beta ' subunit segment contacting the melted region of the lacUV5 promoter

Identification of the RNA polymerase functional regions involved in interac tions with promoter is a basis for understanding the mechanism of transcrip tion initiation. We have used formaldehyde cross-linking to identify a regi on of Escherichia coli RNA polymerase beta' subunit contacting lacUV5 promo ter in open complex. Treatment of open complex with formaldehyde results in cross-linking of beta' and sigma(70) subunits at positions -5 and -3 on th e nontemplate strand of the promoter DNA These cross-links reflect specific interactions between RNA polymerase and promoter established in open compl ex. The positions of formaldehyde cross-links in the beta' subunit were map ped to the N-terminal segment (Cys(198)-Met(237)), which is contiguous to t he evolutionary conserved region B, The proximity of the beta' and sigma cr osslinks suggest that the N-terminal region of the beta' subunit, interacti ng with single-stranded promoter DNA, can cooperate with the sigma subunit in the process of open complex formation.