Using solutes and kinetics to probe large conformational changes in the steps of transcription initiation

Small solutes are useful probes of large conformational changes in RNA polymerase–promoter interactions and other biopolymer processes. In general, a large effect of a solute on an equilibrium constant (or rate constant) indicates a large change in water-accessible biopolymer surface area in the corresponding step (or transition state), resulting from conformational changes, interface formation, or both. Here, we describe nitrocellulose filter binding assays from series used to determine the urea dependence of open complex formation and dissociation with Escherichia coli RNA polymerase and phage λP_R promoter DNA. Then, we describe the subsequent data analysis and interpretation of these solute effects.