Dittrich K, Gu J, Tinder R, Hogan M, Gao X
Center for Biotechnology, Baylor College of Medicine, The Woodlands, Texas 77381.
Biochemistry. 1994 Apr 12;33(14):4111-20. doi: 10.1021/bi00180a003.
The antiparallel purine.purine.pyrimidine DNA triplex, RRY6, which contains a T.C.G inverted triplet in the center of the sequence, was examined by proton and phosphorous two-dimensional NMR spectroscopy. The local conformation of the T.C.G triplet (T4.C11.G18) and the effect of this triplet on the global helical structure were analyzed in detail. The formation of the T.C.G triplet is confirmed by a set of cross-strand NOEs, including unusual cross-strand NOEs between the third strand and the pyrimidine strand as opposed to the purine strand of the duplex. NMR data suggest that the T.C.G triplet may be present in an equilibrium between a non-hydrogen-bonded form and a T(O4)-C(NH2) hydrogen-bonded form and that there is a distortion of the in-plane alignment of the three bases. The flanking G.G.C base triplets are well-defined on the 5'-side of T4, but somewhat interrupted on the 3'-side of T4. The effect of the third strand binding on the Watson-Crick duplex was probed by an NMR study of the free duplex RY6. NMR parameters are affected mostly around the T.C.G inversion site. The perturbations extend to at least two adjacent base triplets on either side. The binding of the third purine strand and the accommodation of a central T.C.G inversion in RRY6 does not require a readjustment in sugar pucker, which remains in the range of C2'-endo. 31P resonances of RRY6 distribute over a range of 2.2 ppm. The H-P coupling patterns of the third strand differ from those of the duplex. General spectral patterns defined by the marker protons of the RRY and YRY triplexes are compared.
反平行嘌呤-嘌呤-嘧啶DNA三链体RRY6，其序列中心包含一个T·C·G反向三联体，通过质子和磷二维核磁共振光谱进行了研究。详细分析了T·C·G三联体（T4·C11·G18）的局部构象以及该三联体对整体螺旋结构的影响。通过一组跨链核Overhauser效应（NOE）证实了T·C·G三联体的形成，包括第三链与嘧啶链之间不寻常的跨链NOE，与双链体的嘌呤链相反。核磁共振数据表明，T·C·G三联体可能以非氢键形式和T（O4）-C（NH2）氢键形式之间的平衡存在，并且三个碱基的面内排列存在扭曲。侧翼的G·G·C碱基三联体在T4的5'侧定义明确，但在T4的3'侧有些中断。通过对游离双链体RY6的核磁共振研究，探讨了第三链结合对沃森-克里克双链体的影响。核磁共振参数主要在T·C·G反向位点周围受到影响。扰动至少延伸到两侧的两个相邻碱基三联体。第三嘌呤链的结合以及RRY6中中心T·C·G反向的容纳不需要糖环构象的重新调整，糖环构象保持在C2'-内向的范围内。RRY6的31P共振分布在2.2 ppm的范围内。第三链的H-P耦合模式与双链体的不同。比较了由RRY和YRY三链体的标记质子定义的一般光谱模式。
