Figure 2.

DDMs for pairs of structures of bovine ribonuclease A. White space in the DDM means that the absolute value of the distance difference (DD) between the corresponding pair of C^α atoms in the two structures (e.g. PDB entries) is greater than 1 Å, black areas mean that the DD is below 0.5 Å and gray areas indicate DDs between 0.5 and 1 Å. Short thick bars or segments of thin double lines along the tops and sides of the triangular matrices denote the positions of helices or β-strands (taken from the PDB file). Distances between neighboring tick marks on the top and left are at intervals of 20 residues. If the DDM name does not show the chain identifier in parentheses after the PDB name then this indicates that either there is only one chain in the unit cell or the first (usually denoted A) chain is used. (a) 1fs3 (wild-type trigonal crystal) versus 1xpt (monomer A of phosphate-free monoclinic crystal) structures (the DDM is denoted 1fs3–1xpt). (b) DDM 1afu(A)–1afu(B): two monomers from the unit cell of 1afu (monoclinic crystal).