Modified phased translation functions and their application to molecular-fragment location.
Direct methods at high resolution have depended on the resolution of atomic like features in the map. At data resolutions more typical for protein structures (2-3 A) individual atoms may not be resolved, so larger features must be identified. At one extreme the whole molecule may be located using the diffraction magnitudes alone by the molecular-replacement method. At the other extreme it is possible to locate individual residues in a well phased map. In this paper an intermediate problem is addressed: the location of multi-residue fragments on the basis of weak phase information. An agreement function based on the mean-squared difference between model and map over a masked region is shown to be more effective than a simple overlap integral, and may be efficiently calculated by Fourier methods. The techniques are compared using poorly phased electron-density maps at approximately 3 A for the proteins RNAse and O6-methylguanine-DNA-methyltransferase.
Department of Chemistry, University of York, Heslington, York YO1 5DD, England. cowtan@yorvik.york.ac.uk
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D000818:Animals; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D005583:Fourier Analysis; D008958:Models, Molecular; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000737:chemistry; D011487:Protein Conformation; D012260:Ribonucleases / Q000737:chemistry
D019853:O(6)-Methylguanine-DNA Methyltransferase; D012260:Ribonucleases