title: NMR studies of triple-strand formation from the homopurine-homopyrimidine deoxyribonucleotides d(GA)4 and d(TC)4.
abstract: The complexes formed by the homopurine and homopyrimidine deoxyribonucleotides d(GA)4 and d(TC)4 have been investigated by one- and two-dimensional 1H NMR. Under appropriate conditions [low pH, excess d(TC)4 strand] the oligonucleotides form a triplex containing one d(GA)4 and two d(TC)4 strands. The homopurine and one of the homopyrimidine strands are Watson-Crick base paired, and the second homopyrimidine strand is Hoogsteen base paired in the major groove to the d(GA)4 strand. Hoogsteen base pairing in GC base pairs requires hemiprotonation of C; we report direct observation of the C+ imino proton in these base pairs. Both homopyrimidine strands have C3'-endo sugar conformations, but the purine strand does not. The major triplex formed appears to have four TAT and three CGC+ triplets formed by binding of the second d(TC)4 strand parallel to the d(GA)4 strand with a 3' dangling end. In addition to the triplexes formed, at least one other heterocomplex is observed under some conditions.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
authors.forename: P
authors.initials: P
authors.lastname: Rajagopal
authors.forename: J
authors.initials: J
authors.lastname: Feigon
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides
chemical_list: D009838:Oligodeoxyribonucleotides