title: Structure of a DNA:RNA hybrid duplex. Why RNase H does not cleave pure RNA.
abstract: The solution structure of the DNA:RNA hybrid duplex d(GTCACATG):r(caugugac) has been determined by means of two-dimensional nuclear Overhauser effect (2D-NOE) spectra, restrained molecular dynamics and full-relaxation matrix stimulation of the 2D-NOE spectra. The DNA:RNA hybrid duplex assumes neither an A-form nor a B-form structure in solution, but an intermediate heteromerous duplex structure. The sugars of the RNA strand have a normal N-type C3'-endo conformation, but the DNA strand sugars have neither N-type nor S-type conformations; instead, they have an unexpected intermediate O4'-endo conformation. The negative x-displacement, as well as the small rise and positive inclination of the base-pairs, resembles A-form morphology but the minor groove width is intermediate between that of A-form and B-form duplexes. Both the DNA and RNA strands show prominent sequence-dependent variations in their helical parameters. Combined analysis of NOE and J-coupling data indicates that the DNA sugars are not in a dynamical two-state equilibrium. The detailed three-dimensional structure of this DNA:RNA hybrid molecule leads to a proposed model for its interaction with RNase H. Several specific structural features of the enzyme complexed with the hybrid duplex appear to explain the mechanism whereby RNase H discriminates between DNA:RNA hybrid duplexes and pure RNA:RNA duplexes.
authors.affiliation: Department of Chemistry, University of Washington, Seattle 98195.
authors.lastname: Fedoroff OYu
authors.forename: M
authors.initials: M
authors.lastname: Salazar
authors.forename: B R
authors.initials: BR
authors.lastname: Reid
mesh_terms: D001483:Base Sequence; D003198:Computer Simulation; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry*; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D009843:Oligoribonucleotides / Q000737:chemistry* / Q000378:metabolism; D016914:Ribonuclease H / Q000737:chemistry / Q000378:metabolism*
chemical_list: D009692:Nucleic Acid Heteroduplexes; D009838:Oligodeoxyribonucleotides; D009843:Oligoribonucleotides; D016914:Ribonuclease H