HOLOGRAPHIC METHODS IN X-RAY CRYSTALLOGRAPHY .4. A FAST ALGORITHM ANDITS APPLICATION TO MACROMOLECULAR CRYSTALLOGRAPHY

The holographic method makes use of partially modeled electron density and experimentally measured structure-factor amplitudes to recover el ectron density corresponding to the unmodeled part of a crystal struct ure. This paper describes a fast algorithm that makes it possible to a pply the holographic method to sizable crystallographic problems. The algorithm uses positivity constraints on the electron density and can incorporate a 'target' electron density, making it similar to solvent flattening. The potential for applying the holographic method to macro molecular X-ray crystallography is assessed using both synthetic and e xperimental data.