Kinetic study in vitro of Escherichia coli promoter closure during transcription initiation.

The rate of closure of two Escherichia coli promoters borne by plasmid pBR322, following transcription initiation from the open complex, was probed in vitro by the protection of unpaired thymines in the open complex against oxidation by KMnO4. Run-off transcription kinetics were also studied under identical conditions. Closure of the open promoter appears to be by far the rate-limiting step of transcription initiation and elongation for the linearized beta-lactamase gene, and is strongly dependent on template topology for the RNAI gene. It is suggested that the corresponding signals are deposited 30 bases at least downstream of transcription initiation and that promoter closure, and its clearance by elongating RNA polymerase, may occur almost simultaneously.