title: Conformational transitions in oriented fibres of the synthetic polynucleotide poly[d(AT)].poly[d(AT)] double helix.
abstract: The synthetic polynucleotide poly[d(AT)].poly[d(AT)] is of interest in studies of the relationship between nucleic acid structure and function. In particular, A + T-rich regions in DNA double helices have been invoked as centres for controlling the transcription of genetic information. Here we describe conditions for observing by X-ray fibre diffraction the A, B, C and D conformations of Na-poly[d(AT)].poly[d(AT)], and for inducing transitions between these conformations. The D form emerges as a particularly stable conformation; once assumed, it persists over a wide range of variation in the relative humidity of the fibre environment. Further, while transitions between the B and D conformations are readily reversible, transitions between A and D are much more complex.
mesh_terms: D009690:Nucleic Acid Conformation; D011067:Poly dA-dT; D011089:Polydeoxyribonucleotides; D012964:Sodium; D013329:Structure-Activity Relationship; D014867:Water; D014961:X-Ray Diffraction
chemical_list: D011089:Polydeoxyribonucleotides; D014867:Water; D011067:Poly dA-dT; D012964:Sodium