title: Proton nuclear magnetic resonance assignments and structural characterization of an intramolecular DNA triplex.
abstract: Two-dimensional 1H n.m.r. spectroscopy has been used to study the 31-base DNA oligonucleotide 5'-dAGAGAGAACCCCTTCTCTCTTTTTCTCTCTT-3', which folds to form a stable intramolecular triplex in solution at acidic pH. This structure is considerably more difficult to assign than short B-DNA duplexes and requires new assignment methods. The assignment strategy and assignments of almost all of the exchangeable and nonexchangeable resonances are presented. Seven base triplets and one Watson-Crick base-pair form the core of the structure and are connected by a four C and four T loop at either end. The second pyrimidine "strand" (bases 24 to 31) in this intramolecular pyrimidine-purine-pyrimidine triplex binds via Hoogsteen base-pairs in the major groove and is parallel to the purine "strand" (bases 1 to 8). Analysis of the sugar puckers reveals that, contrary to widely accepted belief, the triplex sugars are not predominantly in the N-type (close to C3'-endo) conformation. Except for some of the C nucleotides, all sugars are predominantly S-type (close to C2'-endo). Thus, the duplex DNA does not assume N-type sugar conformations to accommodate a third strand in the major groove. A preliminary model of the triplex structure is presented.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
authors.forename: R
authors.initials: R
authors.lastname: Macaya
authors.forename: E
authors.initials: E
authors.lastname: Wang
authors.forename: P
authors.initials: P
authors.lastname: Schultze
authors.forename: V
authors.initials: V
authors.lastname: Sklenár
authors.forename: J
authors.initials: J
authors.lastname: Feigon
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D003855:Deoxyribose / Q000737:chemistry; D006027:Glycosides / Q000737:chemistry; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D011522:Protons; D013696:Temperature
chemical_list: D006027:Glycosides; D009838:Oligodeoxyribonucleotides; D011522:Protons; D003855:Deoxyribose; D004247:DNA