Phase extension to weaker reflections of proteins via a partial structure based tangent formula

When some molecular fragment is well located, the so called partial structure based tangent formula may be used to recovery the complete crystal structure. The formula has been extensively applied to small mole- cules and initial applications to proteins have also been performed. We will show in this paper that the formula may be successfully applied to macromolecules, to refine phase values and to extend the phase information to weak- er reflections, even in absence of prior information (at atomic level) on part of the crystal structure. Experimental tests have been performed via a modified form of the program SIR2000.