Open complex formation during transcription initiation at the Escherichia coli gal P1 promoter: the role of the RNA polymerase [alpha] subunit at promoters lacking an UP-element

We have studied the role of the C-terminal domain of the [alpha] subunit ([alpha]CTD) of Escherichia coli RNA polymerase during transcription initiation at promoters lacking an UP-element. The temperature requirement for open complex formation was used as an indication of the kinetics of this process. We have previously shown that [alpha]CTD is required for transcription initiation at low temperature at the galP1 promoter, a promoter containing an UP-element. DNase I footprinting has been used to reveal the structure of open promoter complexes and the temperature requirement for open complex formation has been determined using potassium permanganate as a probe. In this work we show that, although [alpha]CTD is not absolutely required for transcription initiation at promoters lacking an UP-element, it does play a role during transcription initiation. This role is independent of the sequence of the promoter upstream from the -35 region and does not require stable [alpha]CTD-DNA interactions as determined by DNase I footprinting. The role of [alpha]CTD at promoters lacking an UP-element is discussed.