Open complex formation during transcription initiation at the Escherichia coli galP1 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 a subunit (alpha C TD) of Escherichia coli RNA polymerase during transcription initiation at p romoters lacking an UP-element. The temperature requirement for open comple x formation was used as an indication of the kinetics of this process. We h ave previously shown that alpha CTD is required for transcription initiatio n at low temperature at the galP1 promoter, a promoter containing an UP-ele ment. DNase I footprinting has been used to reveal the structure of open pr omoter 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 transcripti on initiation at promoters lacking an UP-element, it does play a role durin g transcription initiation. This role is independent of the sequence of the promoter upstream from the -35 region and does not require stable alpha CT D-DNA interactions as determined by DNase I footprinting. The role of alpha CTD at promoters lacking an UP-element is discussed.