C. Electrophoretic mobility shift assay (EMSA) showing that CRP protein binds to the vcdRP promoter sequence. Migration of the [32P] end-labeled vcdRP promoter fragment in the absence and presence of increasing concentrations of purified CRP protein (indicated by the black triangle above the gel) was determined by native polyacrylamide gel electrophoresis and autoradiography. The open triangle indicates free DNA whereas the filled triangle indicates VcdRP in complex with CRP. Final concentrations of CRP used in each reaction from left to right (lanes 1-8) were: 0, 0.35, 0.7, 1.4, 2.1, 2.8, 3.5, and 4.2 µM. Radiolabelled DNA and CRP were incubated at 37°C for 20 minutes in buffer containing 0.2 mM cAMP, before being loaded on a 7.5 % non-denaturing polyacrylamide gel. 