Identification of surface residues in the trp repressor of Escherichia coli

A subset of the spin systems assigned in the ¹H NMR spectrum of the trp repressor in the first paper in this series (our penultimate preceding paper in this journal) can be identified as surface or buried residues on the basis of four independent types of measurement: (a) selective spin‐lattice relaxation times; (b) the dependence of line widths on temperature and the concentration of manganous ion; (c) fluorescence quenching; and (d) titration behaviour. Criteria are developed for distinguishing surface and buried residues. The significance for the function of DNA binding proteins is discussed.