A PROCEDURE FOR AB-INITIO PHASING OF ONE-WAVELENGTH ANOMALOUS SCATTERING DATA FROM PROTEINS - COMBINING DIRECT-METHODS WITH THE SOLVENT FLATTENING TECHNIQUE

Both direct methods and the solvent flattening technique have been pro ved capable of breaking the phase ambiguity intrinsic in one-wavelengt h anomalous scattering (OAS) data. However, in theory, while direct me thods are better in deriving starting phases from OAS data, the solven t flattening technique is more powerful in the subsequent phase refine ment. A procedure is described in this paper which combines direct met hods with the solvent flattening technique for phasing of OAS data. Th e procedure has been tested with the known protein RNase Sa. This prot ein is of moderate size, and the diffraction data were collected routi nely without taking special care for the recording of Friedels. The te st proved that the combination of the direct method and the solvent fl attening leads to a much better result than that from either method al one.