DIFFERENT THERMAL-ENERGY REQUIREMENT FOR OPEN COMPLEX-FORMATION BY ESCHERICHIA-COLI RNA-POLYMERASE AT 2 RELATED PROMOTERS

We have studied the effect of temperature on transcription initiation in vitro at two related promoters galP(con) 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, galP(con), 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 -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 galP1 at low temperatures, whereas galP(con) requires higher temperatures. The thermal energy requirement for transcription from preformed open complexes is the same for both promoters.