Poly(dA-dT).poly(dA-dT) in low salt appears to be a left-handed B-helix combined use of chemical theory, fiber diffraction and NMR spectroscopy.
Poly(dA-dT).poly(dA-dT) can adopt the B- and D- forms in the fibrous state. Theoretical energy calculations and fiber diffraction analyses suggest that there can be three structural models of poly(dA-dT).poly(dA-dT) in each of these two forms viz right and left-handed Watson Crick models and left-handed Hoogsteen--a total of six possible models. Fiber data for the polymer in the B- or the D-form or energy calculations cannot distinguish any one model from the other. However, a comparison of observed proton chemical shifts with the theoretically computed ones and the NOE studies on exchangeable and nonexchangeable protons suggest that poly(dA-dT).poly(dA-dT) in low salt solution exists predominantly in the left-handed B-conformation.
D001482:Base Composition; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011067:Poly dA-dT; D011089:Polydeoxyribonucleotides; D013237:Stereoisomerism; D014961:X-Ray Diffraction
D011089:Polydeoxyribonucleotides; D011067:Poly dA-dT