Progress on the direct-methods solution of macromolecular structures using single-wavelength anomalous-dispersion (SAS) data

Abstract

In the past few years, a number of strategies have been outlined to resolve the SAS phase ambiguity given that unique estimates 3(h, k) of the triple invariants are available. A new least-squares method is described that can in principle resolve the phase ambiguity to determine macromolecular phases provided that 3(h, k) estimates are unbiased. Limitations of the method in practical applications are discussed. An example is given where the correct solution can be identi®ed by use of the SAS tangent formula in the instance that traditional SAS phasing methods have lead to an incorrect heavy-atom substructure.

DNA Binding Specificity of Mu Transcription Factor C and Crystallization of C : DNA Complex

“…SAD phasing requires only a single dataset and is made up of (1) finding anomalous scatterers, (2) evaluating initial phases, and (3). phase improvement by density modification algorithms (Hauptman, 1982;La Fortelle, 1997;Cowtan, 1999;Langs et al, 1999;Terwilliger, 2000). Molecular replacement (MR) (Rossmann, 1990) is a technique, which is used when a closely-related structure is available.…”