Chapter 16.3 Ab initio phasing of low-resolution Fourier syntheses

Crystallography of biological macromolecules

Second Online Edition (2012)

Part 16. Direct methods

  1. V. Y. Lunin1,
  2. A. G. Urzhumtsev2,
  3. A. Podjarny3

Published Online: 14 APR 2012

DOI: 10.1107/97809553602060000852

International Tables for Crystallography

International Tables for Crystallography

How to Cite

Lunin, V. Y., Urzhumtsev, A. G. and Podjarny, A. 2012. Ab initio phasing of low-resolution Fourier syntheses. International Tables for Crystallography. F:16:16.3:437–442.

Author Information

  1. 1

    Laboratory of Macromolecular Crystallography, Institute of Mathematical Problems of Biology of the Russian Academy of Sciences, Institutskaia, 4 Region Russia, Pushchino, Moscow Region142290, Russian Federation

  2. 2

    Faculty of Sciences, University of Nancy 1, Vandoeuvre-lès-Nancy, 54506, France

  3. 3

    Structural Biology, IGBMC, BP 163 Cedex, Illkirch, 67404, France

Publication History

  1. Published Online: 14 APR 2012


Low-resolution phasing addresses the cases where experimental X-ray diffraction intensities are only available to a low-resolution limit, or when the standard phasing methods to solve macromolecular structures fail. Ab initio phasing is based on general properties of macromolecular objects (connectivity, electron-density histograms, likelihood of molecular masks etc.) and does not require extra diffraction experiments. The Monte Carlo phasing procedure includes generation of a large ‘population’ of trial solutions, enrichment of this population by filtering with selection criteria, clustering and averaging. The results of low-resolution phasing allow one to get information on the packing of particles in a crystal and on the shape (envelope) of the molecules, and to get an insight into the architecture of multidomain complexes.


  • low-resolution phasing;
  • ab initio phasing;
  • low-resolution images;
  • multifiltering cyclic phasing procedure;
  • map connectivity;
  • few-atoms model;
  • phase averaging;
  • Fourier synthesis;
  • cluster analysis