title: Density constraints and low-resolution phasing.
abstract: Direct phasing needs additional information of a non-specific kind in order to select the correct phase set from all possible ones. This paper analyses the use of constraints which can be formulated in terms of electron-density values. One- and multi-dimensional histograms and connectivity properties are implemented as such constraints in density-modification procedures. These approaches usually cannot unambiguously select the best solution from a set of alternative phase variants. Nevertheless, they do allow the rejection of wrong solutions and the use of cluster analysis and averaging on the remaining variants provide a good starting point for further phase-refinement procedures.
authors.affiliation: LCM3B, UPRESA 7036 CNRS, Faculté des Sciences, Université Henri Poincaré Nancy I, 54506 Vandoeuvre-lès-Nancy, France. sacha@lcm3b.u-nancy.fr
authors.forename: A G
authors.initials: AG
authors.lastname: Urzhumtsev
authors.forename: N L
authors.initials: NL
authors.lastname: Lunina
authors.forename: T P
authors.initials: TP
authors.lastname: Skovoroda
authors.forename: A D
authors.initials: AD
authors.lastname: Podjarny
authors.forename: V Y
authors.initials: VY
authors.lastname: Lunin
mesh_terms: D018360:Crystallography, X-Ray / Q000379:methods*; D004583:Electrons; D005583:Fourier Analysis; D007527:Isoenzymes / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011487:Protein Conformation; D012260:Ribonucleases / Q000737:chemistry*
chemical_list: D007527:Isoenzymes; D012260:Ribonucleases; C077002:ribonuclease Sa3