Differential effect of DNA supercoiling on transcription of adenovirus genes in vitro

We examined the effect of DNA template topology on the transcription of immediate early (E1a), early (E1b) and late (pIX) adenovirus genes in vitro. Transcription in whole cell extracts was measured by quantitative hybridization to end-labelled DNA and protection of hybrids from S1 nuclease digestion. Two- to fourfold more E1a RNA was synthesized from supercoiled, compared to linear, DNA templates. Similarly, transcription of the E1b gene was stimulated three- to sevenfold when the template was supercoiled. In contrast, RNA synthesis from the late pIX gene was found to be independent of DNA topology. These results show that DNA topology affects transcription in a promoter-specific manner.