FINDNCS: a program to detect non-crystallographic symmetries in protein crystals from heavy-atom sites

In order to facilitate applications of averaging techniques in the MIR/MAD procedure, a program, FINDNCS, which automatically identifies non-crystallo graphic symmetry (NCS) from heavy-atom sites, has been developed. The progr am outputs the NCS operations (a rotation matrix and a translation vector), the corresponding root-mean-square (r.m.s) deviations of heavy-atom sites, polar angles and screw translations, and writes coordinates of matching si tes in Protein Data Bank (PDB) format. The program has an interface with th e graphics program O [Jones ct al. (1991). Acta Cryst. A47, 110-119] so tha t the NCS operations can be displayed automatically. In the test examples, all the correct NCS operations were identified and were above the noise sol utions.