Application of direct methods to protein crystallographic phase extension

An alternative formulation of direct methods for phase refinement using the sign probability originally introduced for breaking the phase ambiguity intrinsic in single isomorphous replacement or single-wavelength anomalous diffraction data has been proposed. This formulation can incorporate known phase information through constrained phase refinement. This formulation was tested by application to the phase-extension problem using experimental data. The results showed that this formulation was valid and promising for designing better methods for phase extension.