title: The crystal structure of an alternating RNA heptamer r(GUAUACA) forming a six base-paired duplex with 3'-end adenine overhangs.
abstract: The crystal structure of an alternating RNA heptamer r(GUAUACA) has been determined to 2.0 A resolution and refined to an R(work) of 17.1% and R(free) of 18.5% using 2797 reflections. The heptamer crystallized in the space group C222 with a unit cell of a = 25.74, b = 106.58, c = 30.26 A and two independent strands in the asymmetric unit. Each heptamer forms a duplex with its symmetry-related strand and each duplex contains six Watson-Crick base pairs and 3'-end adenosine overhangs. Therefore, two kinds of duplex (duplex 1 and duplex 2) are formed. Duplexes 1 stack on each other forming a pseudo-continuous column, which is typical of the RNA packing mode, while duplex 2 is typical of A-DNA packing with its termini in abutting interactions. Overhang adenine residues stack within the duplexes with C3'-endo sugar pucker and C2'-endo sugar pucker in duplexes 1 and 2, respectively. A Na+ ion in the crystal lattice is water bridged to two N1 atoms of symmetry-related A7 bases.
authors.affiliation: Department of Chemistry, The Ohio State University, 200 Johnston Laboratory, Columbus, OH 43210, USA.
authors.forename: Ke
authors.initials: K
authors.lastname: Shi
authors.forename: Baocheng
authors.initials: B
authors.lastname: Pan
authors.forename: Muttaiya
authors.initials: M
authors.lastname: Sundaralingam
mesh_terms: D000225:Adenine / Q000737:chemistry*; D020029:Base Pairing; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009843:Oligoribonucleotides / Q000737:chemistry* / Q000235:genetics; D014867:Water / Q000737:chemistry
chemical_list: D009843:Oligoribonucleotides; D014867:Water; D000225:Adenine