The shock of the old: hydrodynamics for the masses

Hydrodynamic techniques such as analytical ultracentrifugation can provide key information about subunit stoichiometry and interaction strengths of protein–nucleic acid interactions. Analysis is complicated by (i) the need for low concentrations in order to observe both free and bound species and (ii) thermodynamic non-ideality. With the introduction of fluorescence optics, we are able to obtain data at lower concentrations, and improved understanding of the statistical thermodynamics of macromolecular solutions has allowed non-ideality to be accurately assigned. With these developments, it is possible now to assay protein–nucleic acid interactions at concentrations typically used in molecular biology assays.