Lac UV5 transcription in vitro. Rate limitation subsequent to formation of an RNA polymerase-DNA complex.

The kinetics of transcription of lac UV5 mRNA using purified DNA restriction fragment as template has been studied. This template, which contains only 203 base pairs, directs the formation of a 67-base lac mRNA with high specificity. The half-time for formation of a DNA-RNA polymerase complex is approximately 0.2 min. However, upon addition of 200 micron nucleoside triphosphates to this complex, RNA production proceeds with a half-time of approximately 1 min. Therefore, it is suggested that the rate-limiting step for lac UV5 mRNA production, under typical in vitro conditions, occurs subsequent to the formation of a promoter-specific complex.