Fig. 2. The structure of the E.coli HPr–IIA^Glc complex. Three sets of superpositions are shown. (A) The structures are best fitted to all the backbone atoms; the backbone and side chains of HPr are shown in green and magenta, respectively, and the backbone and side chains of IIA^Glc are shown in blue and red, respectively. (B) The structures are best fitted to the backbone atoms of IIA^Glc only. (C) The structures are best fitted to the backbone atoms of HPr only. The latter two superpositions illustrate the precision with which the orientation of one molecule is determined relative to the other. Residues from HPr are denoted in italic. The axis of the alignment tensor is shown at the bottom of the figure.