FIG. 4.
The 434 repressor binds DNA in the presence of RNA polymerase at PR. A DNA fragment containing wild-type OR including the PR and PRM promoters was incubated with increasing concentrations of the 434 repressor in the absence (A) or the presence (B) of 50 nM RNA polymerase. Shown is a native gel of the resulting complexes. (A) OR-containing DNA incubated in the absence (lane 1) or the presence (lanes 2 to 7) of increasing concentrations of the 434 repressor. The concentration of the repressor was increased in 2.5-fold steps starting at 100 nM. (B) OR-containing DNA incubated in the absence (lane 1) or the presence of RNA polymerase (lane 2) or RNA polymerase and increasing concentrations of the 434 repressor (lanes 3 to 8). In lanes 3 to 8, RNA polymerase was added to the labeled DNA fragment, and this allowed the formation of an open complex at PR by incubation for 10 min at 37°C. Subsequently, the repressor was added and the mixture was incubated at 37°C for an additional 10 min before addition of heparin and loading on the gel. RNAP, RNA polymerase.