The crystallographic symmetry test for the correctness of a set of phases

Acta Crystallogr A. 2003 Jan;59(Pt 1):28-33. doi: 10.1107/s0108767302018810. Epub 2002 Dec 21.


One of the most important problems in the application of direct methods for large structures is to establish reliable consistency criteria for the correctness of a phasing trial. The introduction in the twin variables method [Bethanis, Tzamalis, Hountas, Mishnev & Tsoucaris (2000). Acta Cryst. A56, 105-111] of a new criterion based on the crystallographic symmetry consists of testing the phase extension and refinement algorithm by deliberately sacrificing the space-group-symmetry information in the auxiliary variable set then using its gradual re-appearance as a criterion for correctness. In the present paper, the crystallographic symmetry test has been used in the implementation of the twin algorithm in two different ways: (i) as an overall test throughout the iterations that is likely to reflect the correctness of the phasing procedure for each one of the extension trials in a macromolecular phasing environment; (ii) as a convenient criterion to determine the optimum cycle for freeing the initial phases used by the algorithm for the phase-extension procedure.

MeSH terms

  • 3-Oxoacyl-(Acyl-Carrier-Protein) Reductase
  • Alcohol Oxidoreductases / chemistry
  • Crystallography, X-Ray / methods*
  • Models, Chemical
  • Proteins / chemistry
  • Ribonuclease T1 / chemistry


  • Proteins
  • Alcohol Oxidoreductases
  • 3-Oxoacyl-(Acyl-Carrier-Protein) Reductase
  • Ribonuclease T1