Reciprocal-space molecular-replacement averaging.

The molecular-replacement equations, in which electron-density averaging and skew averaging have been unified, were used in reciprocal space to refine and extend the resolution of phased reflections. A procedure has been developed for the treatment of molecular envelopes of general shape. The equations were successfully applied to the reflection data of bacteriophage phiX174 (60-fold redundancy). Truncation of the G diffraction function beyond the first few nodes did not have a significant effect on the quality of the molecular-replacement equations. Reciprocal-space molecular-replacement averaging should prove to be a useful alternative to real-space averaging. Strategies are discussed that are possible only in reciprocal space.