CRUNCH: a phase refinement program for high-resolution macromolecular structures

A phase refinement program for high-resolution macromolecular structures is described. The mean phase error of an initial structural solution can often be as large as 60° prior to attempting a refinement, but the CRUNCH program procedure may allow one to reduce this phase error to 10 or 20° for all data prior to actually inspecting any map to see how well it may fit a structural model. The procedure is similar to the real/reciprocal space refinement loop incorporated in the half-baked algorithm described by Sheldrick [Sheldrick & Gould (1995). Acta Cryst. B51, 423-431.] Refinement results are presented for nine different structures which diffract to better than 1.2 Å resolution. The program and test data are available via anonymous ftp (nexus.hwi.buffalo.edu).