Vorlícková M, Sági J, Szabolcs A, Ebinger K, Fellegvári I, Kypr J
Institute of Biophysics, Czechoslovak Academy of Sciences, Brno.
J Biomol Struct Dyn. 1993 Feb;10(4):681-92. doi: 10.1080/07391102.1993.10508000.
We have synthesized poly(dA,dPu-dT) and poly(dA,n2dPu-dT) containing, respectively, 5.7% of purine and 7.4% of amino2purine in place of adenine to demonstrate that these apparently negligible perturbations of the primary structure have dramatic consequences for the polynucleotide conformational isomerizations. The replacement of adenine by amino2purine, preserving the number of hydrogen bonds between the complementary bases, has a stronger effect on the polynucleotide conformational isomerizations than the replacement with purine that is bound only by a single hydrogen bond to thymine. Nevertheless, poly(dA,dPu-dT) forms a more thermostable duplex than poly(dA,n2dPu-dT). Furthermore the few amino2purines in poly(dA,n2dPu-dT) inhibit its isomerization into X-DNA, stabilize but modify A-DNA and stabilize Z-DNA. Kinetics of the B-Z transition of poly(dA,n2dPu-dT) is fast to indicate that the amino groups in the double helix minor groove substantially decrease the kinetic barrier between B- and Z-DNA. On the other hand, the replacement of adenine by purine destabilizes both Z-DNA and A-DNA, and the destabilization of X-DNA is weaker than with amino2purine. A-form and B-form perhaps coexist in poly(dA,dPu-dT) at high concentrations of ethanol.
我们合成了分别含有5.7%嘌呤和7.4%氨基嘌呤取代腺嘌呤的聚（dA，dPu-dT）和聚（dA，n2dPu-dT），以证明这些一级结构中看似微不足道的扰动对多核苷酸构象异构化具有显著影响。用氨基嘌呤取代腺嘌呤，保持互补碱基之间的氢键数量，对多核苷酸构象异构化的影响比仅通过单个氢键与胸腺嘧啶结合的嘌呤取代更强。然而，聚（dA，dPu-dT）形成的双链体比聚（dA，n2dPu-dT）更耐热。此外，聚（dA，n2dPu-dT）中少量的氨基嘌呤会抑制其异构化为X-DNA，稳定但改变A-DNA并稳定Z-DNA。聚（dA，n2dPu-dT）的B-Z转变动力学很快，表明双螺旋小沟中的氨基大大降低了B-DNA和Z-DNA之间的动力学障碍。另一方面，用嘌呤取代腺嘌呤会使Z-DNA和A-DNA都不稳定，并且X-DNA的不稳定程度比用氨基嘌呤时弱。在高浓度乙醇中，聚（dA，dPu-dT）中可能同时存在A-型和B-型。
