Different thermal energy requirement for open complex formation by Escherichia coli RNA polymerase at two related promoters.

We have studied the effect of temperature on transcription initiation in vitro at two related promoters ga/Pcon and ga/P1, which have the same nucleotide sequence around the -10 region and transcription start site, but differ in upstream sequences. One of the promoters, ga/Pcon, carries the consensus -35 hexamer, 5'TTGACA 3', whilst ga/P1 contains a block of 'distortable' upstream sequences that allow promoter function in the absence of a -35 region consensus sequence. RNA polymerase can form complexes with both promoters at a range of temperatures. However, the thermal energy requirement for open complex formation differs: open complexes can form at ga/P1 at low temperatures, whereas ga/Pcon requires higher temperatures. The thermal energy requirement for transcription from preformed open complexes is the same for both promoters.