title: Structures for polyinosinic acid and polyguanylic acid.
abstract: X-ray-diffraction analysis of oriented, partially crystalline fibres of polyinosinic acid has resulted in a new molecular model. This model consists of four identical polynucleotide chains related to one another by a fourfold rotation axis. The coaxial helices are righthanded (screw symmetry 23(2)) and have an axial translation per residue h=0.341nm and a rotation per residue t=31.3 degrees . Incorporated in the model are standard bond lengths, bond angles and C-2-endo furanose rings. The nucleotide conformation angles, determined by linked-atom least-squares methods, are orthodox and the fit with the X-ray intensities is good. Each hypoxanthine base is linked to two others by hydrogen bonds involving O-6 and N-1. Further stability may arise from intrachain hydrogen bonds between each ribose hydroxyl group and the phosphate oxygen O-3. If guanine were to be substituted for hypoxanthine in an isogeometrical molecular structure, additional hydrogen bonds could be made between every N-2 and N-7.
mesh_terms: D006150:Guanine Nucleotides; D006157:Guanosine Monophosphate; D007042:Hypoxanthines; D007291:Inosine Monophosphate; D007292:Inosine Nucleotides; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011119:Polynucleotides; D014961:X-Ray Diffraction
chemical_list: D006150:Guanine Nucleotides; D007042:Hypoxanthines; D007292:Inosine Nucleotides; D011119:Polynucleotides; D007291:Inosine Monophosphate; D006157:Guanosine Monophosphate