title: Structure of poly (dT).poly (dA).poly (dT).
abstract: The molecular structure of poly (dT).poly (dA).poly (dT) 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 DNA. The final R-value for the preferred structure is 0.29 significantly lower than that for plausible alternatives. The molecule forms a 12-fold right-handed triple-helix of pitch 38.4 A and each base triplet is stabilized by a set of four Crick-Watson-Hoogsteen hydrogen bonds. The deoxyribose rings in all the three strands have C2'-endo conformations. The grooveless cylindrical shape of the triple-helix is consistent with the lack of lateral organization in the fiber.
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*; D008958:Models, Molecular; D015233:Models, Statistical; D009690:Nucleic Acid Conformation; D011061:Poly A / Q000737:chemistry*; D011071:Poly T / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: C051802:triplex DNA; D011061:Poly A; D011071:Poly T; C015465:poly(dA); D004247:DNA