title: A new model for DNA containing A.T and I.C base pairs.
abstract: DNA polymers containing exclusively A.T or I.C base pairs frequently exhibit D- or E-type X-ray diffraction patterns when dried. The distribution of intensities in fiber patterns appears to demand helical structures with 7 and 7.5 bp/turn, respectively, but it is not stereochemically possible to wind a right-handed antiparallel B-family helix this tightly. It is a simple matter, however, to build a left-handed helix with 7-7.5 bp/turn by incorporating Hoogsteen pairing into a Z helix framework. X-ray intensities calculated from this novel left-handed Hoogsteen model provide as reasonable a fit to the D-DNA diffraction pattern as do intensities calculated from previously proposed right-handed 8-fold models.
mesh_terms: D000225:Adenine; D001482:Base Composition; D003596:Cytosine; D004247:DNA; D007288:Inosine; D008957:Models, Genetic; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D013941:Thymine; D014961:X-Ray Diffraction
chemical_list: D007288:Inosine; D003596:Cytosine; D004247:DNA; D000225:Adenine; D013941:Thymine