title: Bimolecular DNA triplexes: duplex extensions show implications for H-form DNA stability.
abstract: H-form DNA has recently been shown to be biologically relevant by its involvement in the process of homologous recombination [Kohwi, Y. , and Panchenko, Y. (1993) Genes Dev. 7, 1766-1778]. A bimolecular DNA triple-stranded structure (triplex) is central to the formation of H-form DNA. Understanding the formation and factors governing the stability of such bimolecular triplexes is necessary to fully elucidate the structure/function relationship of H-form DNA. In this study, we extend known information on bimolecular triplexes by examining the effect of a variable CNC base triad (where N = A, C, T, or G) on a 10 base triad triplex that mimics the triplex motif in H-form DNA. We also examine the effect that a duplex extension of four base pairs has on triplex stability and selectivity for the base N. Results from thermal denaturation experiments indicate that the fully complementary triplex is more stable than its duplex counterpart (DeltaTm = 13 degrees C) and is resistant to degradation by bovine spleen phosphodiesterase for at least 24 h at 10 degrees C. A single-base mismatch in the purine strand of the triplex structure is destabilizing (DeltaTm = approximately 20 degrees C), and all structures containing a mismatch were readily degraded by bovine spleen phosphodiesterase. An extension of four duplex base pairs onto the triplex structure affects the stability of the DNA complex and may have implications relevant to H-form DNA.
authors.affiliation: Department of Biochemistry, Washington State University, Pullman, Washington 99164-4660, USA.
authors.forename: A A
authors.initials: AA
authors.lastname: Mundt
authors.forename: G J
authors.initials: GJ
authors.lastname: Crouch
authors.forename: B E
authors.initials: BE
authors.lastname: Eaton
mesh_terms: D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D002417:Cattle; D004247:DNA / Q000737:chemistry*; D004355:Drug Stability; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D010727:Phosphoric Diester Hydrolases; D013154:Spleen; D013816:Thermodynamics
chemical_list: D009838:Oligodeoxyribonucleotides; C051802:triplex DNA; D004247:DNA; D010727:Phosphoric Diester Hydrolases