Integration of Direct Methods With Macromolecular Crystallographic Techniques

The role of direct methods in macromolecular crystallography is discussed. The common belief that such methods will still remain marginal is rejected. Different sectors are analyzed. A direct procedure for phasing reflections when diffraction data of one isomorphous derivative are available is briefly described. The applications to experimental data of some test structures succeeded, and suggest that direct methods are competitive with traditional SIR techniques. Attention is also devoted to a formula which is able to recover the total from a partial structure. Direct methods can play a central role also for expanding (and refining) phases from derivative to native resolution, and can constitute an alternative to traditional molecular replacement techniques.