On symmetries of substructures.

This paper accompanies a lecture given at the 2003 CCP4 Study Weekend on experimental phasing. With the audience of the CCP4 Study Weekend in mind, an overview is given of symmetries of substructures and the implications for single isomorphous replacement and single anomalous diffraction phasing procedures, as well as difference Fourier analyses. Pointers are also provided to practical tools for working with substructure symmetries.