Transcription of colicin E1 plasmid: electron-microscopic mapping of promoters

The promoters of ColE1 plasmid DNA have been localized. Their position has been determined relative to the functional map of the plasmid. The direction of transcription from each promoter has been established. Superhelical ColE1 DNA was transcribed in vitro by Escherichia coli RNA polymerase. The resulting complexes of DNA with nascent RNA were treated with restriction endonucleases EcoR1 and SmaI and observed in an electron microscope. Statistical analysis of RNA distribution on DNA made it possible to localize the promoters and determine the direction of transcription from them. The analysis was based on a specially prepared computer program.