Open AccessBASE PAIRING IN 5-CHLOROURIDINE
Author(s) -
Charles L. Coulter,
S. W. Hawkinson
Publication year - 1969
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.63.4.1359
Subject(s) - polynucleotide , hydrogen bond , crystallography , chemistry , alkane stereochemistry , glycosidic bond , monoclinic crystal system , molecule , nucleoside , stereochemistry , crystal structure , dihedral angle , base pair , nucleic acid , dna , biochemistry , organic chemistry , enzyme
5-Chlorouridine has been found to crystallize from water with the molecules of the nucleoside arranged in a base-paired, parallel-stranded ribbon. This type of polymer structure has not been previously considered for nucleic acids. We have constructed a model of polyuridylic acid based upon the 5-chlorouridine crystal structure and wish to suggest it as a plausible molecular complex for this and perhaps other polynucleotides. The crystals are monoclinic, space group P21 , witha = 7.536 A,b = 5.790 A,c = 13.219 A, and β = 99.89°. There are two 5-chlorouridine molecules per cell. The nucleoside bases are linked across a 21 axis with hydrogen bonds between N(3) and O(4). The hydrogen bond length is 2.85 A. The conformation of the base with the ribose about the β-glycosidic bond isanti , with a torsion angle relative to O (1′) of -59.8°. The sugar puckering is C(2′)-endo , and the conformation about the C(4′)—C(5′) bond isgauche-gauche . To build the polymer model, the C(4′)—C(5′) bond was rotated 100° and the sugar-base torsion angle adjusted to -30°. This brought O(3′) and O(5′) of adjacent sugars close enough to make the phosphate ester linkage found in polynucleotides.