title: Structure of Poly (U).poly (A).poly (U).
abstract: The molecular structure of poly (U).poly (A).poly (U) has been determined and refined using the continuous x-ray intensity data on layer lines in the diffraction pattern obtained from an oriented fiber of the RNA. The final R-value for the preferred structure is 0.24, far lower than that for the plausible alternatives. The polymer forms an 11-fold right-handed triple-helix of pitch 33.5A and each base triplet is stabilized by Crick-Watson-Hoogsteen hydrogen bonds. The ribose rings in the three strands have C3'-endo, C2'-endo and C2'-endo conformations, respectively. The helix derives additional stability through systematic interchain hydrogen bonds involving ribose hydroxyls and uracil bases. The relatively grooveless cylindrical shape of the triple-helix is consistent with the lack of lateral organization.
authors.affiliation: Whistler Center for Carbohydrate Research, Purdue University, West Lafayette, IN 47907, USA. chandra@purdue.edu
authors.forename: R
authors.initials: R
authors.lastname: Chandrasekaran
authors.forename: A
authors.initials: A
authors.lastname: Giacometti
authors.forename: S
authors.initials: S
authors.lastname: Arnott
mesh_terms: D004247:DNA / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015233:Models, Statistical; D009690:Nucleic Acid Conformation; D011061:Poly A / Q000737:chemistry*; D011072:Poly U / Q000737:chemistry*; D012266:Ribose / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: C051802:triplex DNA; D011061:Poly A; D011072:Poly U; D012266:Ribose; D004247:DNA