Figure 1.

Dependence of promoter activity on superhelical density and Eco SSB. (A) Diagram of the 2.2-kb DNA circles used for transcriptional studies. The sequence of the template strand of promoters P1 and P2 is shown below. (B) Transcription on templates of different superhelical densities in the absence (left) and presence (right) of Eco SSB. (C) Eco SSB activation of transcription on templates of different superhelical densities. RNAs synthesized in in vitro transcription assays using topoisomers of N4 early promoter-containing DNA circles as templates were analyzed on denaturing gels. The two major transcripts, initiated from P1 or P2 and terminated at the strong terminator t2, are marked at right.