FIGURE 4.

Electrophoretic mobility shift assays show that the NmFNR-DNA complex is relatively oxygen resistant. A, NmFNR was treated with oxygen for various periods and then allowed to complex with DNA containing a consensus FNR site, prior to separating DNA-containing fragments by 8% acrylamide electrophoresis and staining gels for DNA with ethidium bromide. Lane 1, DNA only; lane 2, anaerobic NmFNR and DNA; lanes 3–6, NmFNR made aerobic for 1, 5, 30, and 60 min, respectively, then allowed to complex with DNA. Free DNA is indicated with an asterisk, and an arrowhead indicates where a protein-DNA complex forms for anaerobic NmFNR and NmFNR made aerobic for 1–5 min but not longer periods. The same procedure was followed for B as in A except that the NmFNR-DNA complex was generated prior to treatment with oxygen. An FNR-DNA complex persists after 30 or 60 min under aerobic conditions. Reactions consisted of 10 μl of FNR (92.5 μm, assuming binding as a dimer) and 10 μl of DNA (100 μm duplex) either mixed for 30 min anaerobically prior to O₂ exposure (B) or the DNA was added after each time point subsequent to the aerobic exposure of FNR (A).