Stimulation of yeast RNA polymerase II transcription by critical values of supercoiling

RNA chains of discrete length were obtained in vitro by yeast RNA polymerase II directed transcription of a supercoiled plasmid. On the basis of the amount and the molecular weight of the RNA chains synthesized in the absence of reinitiation events, the number of actively transcribing RNA polymerase molecules has been calculated. A stimulation of transcriptional activity was found to be related to the torsional strength of negative supercoiling of the template. The DNA unwinding angle measured in the complexes formed with the enzyme in the presence of three ribonucleoside triphosphates equals 485 +/- 30 degrees, marking a melting effect of 14 base pairs per bound enzyme molecule.