On the application of direct methods to oligonucleotide crystallography.

The direct methods program SAYTAN was applied to simulated data at various resolutions from three oligonucleotides. Success in solving the structures was found to depend more upon the resolution of the data than upon errors in the data or the complexity of the structure. Collecting the data at a reduced temperature has little effect, unless it alters the mosaicity of the crystal or changes the resolution of the data. The presence of a heavy atom dramatically improved the phase refinement, particularly at low resolution.