Ab initio phasing of low‐resolution Fourier syntheses

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