title: Structural polymorphism in d(T)12.d(A)12*d(T)12 triple helices.
abstract: DNA triple helices containing two thymine strands and one adenine strand have been studied, using model building followed by energy minimisation, for different orientations of the third strand resulting from variation in the hydrogen bonding between the Watson-Crick duplex and the third strand and the glycosidic torsion angle in the third strand. Our results show that the structure with a parallel orientation of the third strand, in which the third strand base forms Hoogsteen hydrogen bonds with the adenine base in the Watson-Crick duplex, is energetically the most favourable. An antiparallel orientation of the third strand is also possible, in which the third strand base hydrogen bonds to both the bases in the Watson-Crick duplex. This structure is energetically comparable to the parallel structure. For the parallel triplex a 200ps molecular dynamics simulation starting from two different starting structures indicates that at 300K significant structural heterogeneity exists in this triplex structure. The results are compared with existing structural data on this class of triplexes derived from theoretical and NMR techniques.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India.
authors.forename: M R
authors.initials: MR
authors.lastname: Kiran
authors.forename: M
authors.initials: M
authors.lastname: Bansal
mesh_terms: D001482:Base Composition; D004247:DNA / Q000737:chemistry*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation
chemical_list: D004247:DNA