Figure 4.

In vitro transcription from and open complex formation on ecl18kI promoters. Escherichia coli RNAP σ⁷⁰ holoenzyme was combined with a DNA fragment containing the entire ecl18kI intergenic region and flanking sequences in the presence, where indicated, of M.Ecl18kI (the latter was added before RNAP in lanes labelled with an asterisk). In (A), a single round of transcription was allowed to occur by supplementing the reactions with a mixture of NTPs and heparin. In (B), promoter complexes were probed with KMnO₄. Reaction products were resolved by denaturing polyacrylamide gel electrophoresis and revealed by autoradiography. Area protected from DNase I cleavage by M.Ecl18kI is shown as a dark rectangle at the right hand side of the gel of (B).