Anomalous signal of phosphorus used for phasing DNA oligomer: importance of data redundancy

The crystal structure of a left-handed Z-DNA hexamer duplex d(CGCGCG)(2) ha s been solved based on the anomalous diffraction signal of inherent P atoms using data collected at the single wavelength of 1.54 Angstrom. The anomal ous signal of about 2% of the total diffracted intensity, constant for all nucleic acids, may be generally useful for solving crystal structures of DN A and RNA oligomers. The multiplicity of intensity measurements is shown to crucially affect the data quality and the ability to solve the phase probl em. The anisotropic model refined to an R factor of 8.9% at 0.95 Angstrom r esolution.