Résumé
Identification of the RNA polymerase functional regions involved in interactions with promoter is a basis for understanding the mechanism of transcription initiation. We have used formaldehyde cross-linking to identify a region of Escherichia coli RNA polymerase β′ subunit contacting lacUV5 promoter in open complex. Treatment of open complex with formaldehyde results in cross-linking of β′ and ς70 subunits at positions −5 and −3 on the nontemplate strand of the promoter DNA. These cross-links reflect specific interactions between RNA polymerase and promoter established in open complex. The positions of formaldehyde cross-links in the β′ subunit were mapped to the N-terminal segment (Cys198–Met237), which is contiguous to the evolutionary conserved region B. The proximity of the β′ and ς cross-links suggest that the N-terminal region of the β′ subunit, interacting with single-stranded promoter DNA, can cooperate with the ς subunit in the process of open complex formation.