Different thermal energy requirement for open complex formation byEscherichia coliRNA polymerase at two related promoters

Abstract
We have studied the effect of temperature on transcription initiation in vitro at two related promoters galPcon and galP1, which have the same nucleotide sequence around the −10 region and transcription start site, but differ in upstream sequences. One of the promoters, galPcon, carries the consensus -35 hexamer, 5′TTGACA 3′, whilst galP1 contains a block of ‘distortable’ upstream sequences that allow promoter function in the absence of a −3 5 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 galP1 at low temperatures, whereas galPcon requires higher temperatures. The thermal energy requirement for transcription from preformed open complexes is the same for both promoters.