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

摘要: INTEREST in triple and quadruple DNA helices built from homopurine homopyrimidine strands has recently intensified principally because such structures may occur vivo1 but also of the potential use triplexes both forming highly sequence-specific complexes for chromosome mapping2,3 repressing transcription4. From fibre diffraction data, models triplex with poly(U)·poly(A)·poly(U) poly(dT)·poly(dA)·poly(dT) have been proposed5, which purine one pyrimidine strand are Watson–Crick paired an A' helix, other is Hoogsteen base-paired parallel to along major groove. A similar base-pairing scheme involving G C would require protonation base-pair formation, proposed1,6 by analogy single-sequence data. To date, however, there no single crystal or NMR structural data on triplexes, direct observation protonated a context. We present here first evidence formation d(G-A)4 d(T-C)4 oligonucleotides, report imino protons cytosines triplex.