In vitro transcription by purified yeast RNA polymerase II. Coarse promoter mapping on homologous cloned genes.

Clones of the yeast Tyl element and 2 microns plasmid have been selectively transcribed in vitro by partially or completely purified yeast RNA polymerase II. Electrophoretic analysis of whole and restricted ternary transcription complexes allows the localization of the in vitro actively transcribed regions of the analyzed genes. The DNA regions that actively promote in vitro transcription correspond to the nucleotide sequence that in the Tyl element encompasses the in vivo transcription initiation sites and that in the 2 micrometer plasmid encompasses the starting codons of two oppositely oriented potential protein coding frames. The transcription assay that we describe herein may be applied to analyze rapidly the in vitro transcription of clones genes, to localize transcription initiation sites on supercoiled templates and to evaluate the differential in vitro promoter strength in RNA polymerase II served genes. Data obtained with RNA polymerase II at two different stages of purification are presented in parallel. Studies with a completely purified enzyme should certainly be preferred although the use of a partially purified RNA polymerase II may be convenient and may reveal factors which affect specificity.