Journal Article

Triple-strand formation in the homopurine:homopyrimidine DNA oligonucleotides d(G-A)4 and d(T-C)4

Rajagopal, Ponni, Feigon, Juli

1989

Overview

INTEREST in triple and quadruple DNA helices built from homopurine and homopyrimidine strands has recently intensified principally because such structures may occur in vivo 1 but also because of the potential use of triplexes both in forming highly sequence-specific complexes for use in chromosome mapping 2,3 and in repressing transcription 4 . From fibre diffraction data, models for triplex structures with poly(U)·poly(A)·poly(U) and poly(dT)·poly(dA)·poly(dT) have been proposed 5 , in which the purine and one pyrimidine strand are Watson–Crick paired in an A' helix, and the other pyrimidine strand is Hoogsteen base-paired parallel to the purine strand along the major groove. A similar base-pairing scheme involving G and C would require protonation of C for Hoogsteen base-pair formation, and models for such triplexes have been proposed 1,6 by analogy to the single-sequence fibre diffraction data. To date, however, there have been no single crystal or NMR structural data on DNA triplexes, and no direct observation of the protonated C in such a context. We present here the first NMR evidence for triplex formation in DNA from the homopurine d(G-A) 4 and homopyrimidine d(T-C) 4 oligonucleotides, and report direct observation of imino protons from protonated cytosines in the triplex.

• Publisher: Nature Publishing Group UK,Nature Publishing
• Subject: Analytical, structural and metabolic biochemistry / Base Sequence / Biological and medical sciences / DNA / Dna, deoxyribonucleoproteins / Fundamental and applied biological sciences. Psychology / Humanities and Social Sciences / letter / Magnetic Resonance Spectroscopy / Molecular Sequence Data / Molecular Structure / multidisciplinary / Nucleic Acid Conformation / Nucleic acids / Oligodeoxyribonucleotides / Science / Science (multidisciplinary)