Molecular modelling has been used to probe the conformational preferences of double stranded DNA-RNA hybrids. As might be expected, the sugars of the DNA strand have higher conformational flexibility, but, for the majority of the repetitive sequences studied, these sugars prefer a C2-endo pucker, while ribose sugars uniformly adopt a C3-endo pucker. This gives rise to a strongly heteronomous duplex conformation. One exception to this rule involves the thymidine strand of poly(dT).poly(rA), which marginally prefers a C3-endo pucker. Our study further indicates that the DNA strands of the hybrids favour backbone torsions in the canonical B domain, rather than the modified values proposed on the basis of fibre diffraction studies. Backbone conformational transitions can nevertheless be induced leading to an alpha gamma-flip (alpha:gamma, g-/g(+)-->t/t) or to the alpha beta gamma-flip form proposed from fibre studies (alpha:beta:gamma, g-/t/g(+)-->t/g+/t). The latter transition is also found to be linked to BI-->BII transitions (epsilon:zeta, t/g(-)-->g-/t).
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机译：分子模型已被用来探测双链DNA-RNA杂种的构象偏好。可以预料，DNA链的糖具有更高的构象柔韧性，但是，对于大多数重复序列研究，这些糖更喜欢C2内折叠，而核糖则统一采用C3内折叠。这产生了高度异质的双链体构象。该规则的一个例外情况是poly（dT）.poly（rA）的胸苷链，略微偏爱C3内折叠。我们的研究进一步表明，杂合体的DNA链有利于规范B结构域的骨架扭曲，而不是基于纤维衍射研究提出的修正值。尽管如此，仍可以诱导骨干构象转变，从而导致αγ翻转（alpha：γ，g- / g（+）-> t / t）或纤维研究提出的αbetaγ翻转形式（alpha：beta ：gamma，g- / t / g（+）-> t / g + / t）。还发现后一个过渡与BI-> BII过渡有关（epsilon：zeta，t / g（-）-> g- / t）。
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