Acta Crystallographica Section D

Biological Crystallography

Volume 58, Part 12 (December 2002)


short communications



Acta Cryst. (2002). D58, 2213-2215    [ doi:10.1107/S0907444902016384 ]

Rapid automatic NCS identification using heavy-atom substructures

T. C. Terwilliger

Abstract: An important component of a fully automated system for structure solution and phase improvement through density modification is a capability for identification of non-crystallographic symmetry as early in the process as possible. Algorithms exist for finding NCS in heavy-atom sites, but currently require of the order of N5 comparisons to be made, where N is the number of sites to be examined, including crystallographically related locations. A method described here based on considering only sets of sites that have common interatomic distances reduces the computational time by several orders of magnitude. Additionally, searches for proper symmetry allow the identification of NCS in cases where only one heavy atom is present per NCS copy.

Keywords: non-crystallographic symmetry; heavy-atom substructures.

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