title: Geometric properties of nucleic acids with potential for autobuilding.
abstract: Medium- to high-resolution X-ray structures of DNA and RNA molecules were investigated to find geometric properties useful for automated model building in crystallographic electron-density maps. We describe a simple method, starting from a list of electron-density 'blobs', for identifying backbone phosphates and nucleic acid bases based on properties of the local electron-density distribution. This knowledge should be useful for the automated building of nucleic acid models into electron-density maps. We show that the distances and angles involving C1' and the P atoms, using the pseudo-torsion angles \eta' and \theta\,' that describe the ...P-C1'-P-C1'... chain, provide a promising basis for building the nucleic acid polymer. These quantities show reasonably narrow distributions with asymmetry that should allow the direction of the phosphate backbone to be established.
authors.affiliation: Department of Structural Chemistry, Georg-August-University Göttingen, Tammanstrasse 4, D-37077 Göttingen, Germany. tg@shelx.uni-ac.gwdg.de
authors.forename: Tim
authors.initials: T
authors.lastname: Gruene
authors.forename: George M
authors.initials: GM
authors.lastname: Sheldrick
mesh_terms: D018360:Crystallography, X-Ray; D004247:DNA / Q000032:analysis / Q000737:chemistry*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009696:Nucleic Acids / Q000032:analysis / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D012313:RNA / Q000032:analysis / Q000737:chemistry*
chemical_list: D009696:Nucleic Acids; D010710:Phosphates; D012313:RNA; D004247:DNA