HKL2MAP: a graphical user interface for macromolecular phasing with SHELX programs

One approach to phasing of macromolecular crystal structure is to exploit the small changes in diffracted intensities induced by the inclusion of heavy atoms, to alter the wavelength in the presence of anomalous scatterers, or to use a combination thereof. In the SHELX suite of crystallographic programs, the computations involved in the respective phasing procedures are divided into three steps: (i) extraction of structure factors representing the substructure of heavy atoms and/or anomalous scatterers only (SHELXC; Sheldrick, 2004), (ii) determination of the substructure (SHELXD; Schneider & Sheldrick, 2002), (iii) calculation of initial phases based on the knowledge of the substructure and improvement of these phases by density modi®cation (SHELXE; Sheldrick, 2002). A number of crystal structures have been solved using the combination of the programs mentioned above. However, in particular for the inexperienced user, the creation of correct input ®les and the interpretation of the intermediate results can be a major obstacle.