CONFORMATIONAL PROPERTIES OF THE G-BULLET-G MISMATCH IN D(CGCGAATTGGCG)2 DETERMINED BY NMR
CONFORMATIONAL PROPERTIES OF THE G-BULLET-G MISMATCH IN D(CGCGAATTGGCG)2 DETERMINED BY NMR
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DOI：
10.1021/bi00138a024
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发表时间：
1992-06-16
期刊：
影响因子：
2.9
通讯作者：
LANE, AN
中科院分区：
文献类型：
--
作者：
BORDEN, KLB;JENKINS, TC;LANE, AN
用H-1和P-31核磁共振研究了含有两个不互补的G.G碱基对的DNA双链d(CGCGAATTGGCG)2在水溶液中的构象性质与温度的关系。G-G不匹配是高度不稳定的，其T(m)值比原生EcoRI十二聚体的T(m)值低35 K。十二聚体在核磁共振光谱中呈现对称，并且主要以平均b型DNA构象存在。然而，H-1和P-31核磁共振谱表明，不匹配的核苷酸及其最近邻的构象不均匀性显著增加，随着温度的升高。没有证据表明存在显著的同嘌呤构象。错配碱基G4和G9的亚质子是简并的，在高场下共振，并且容易与溶剂交换。这些结果表明错配的碱基仅是弱氢键，并且仅部分堆积在螺旋结构中。当温度升高时，双相显示出源自错配位点的两个或多个构象之间的交换增加。然而，这些额外的构象保持了沃森-克里克氢键。化学交换的增加与G.G位提供局部核的准熔融过程是一致的。通过动态退火进行的大量建模研究证实了G（反）-G（反）构象是有利的，并且错配对在螺旋内的堆叠很差。结果解释了该双相的热稳定性差和低低显色性。
The conformational properties of the DNA duplex d(CGCGAATTGGCG)2, which contains two noncomplementary G.G base pairs, have been examined in aqueous solution by H-1 and P-31 NMR as a function of temperature. The G-G mismatch is highly destabilizing, with a T(m) value 35 K below that observed for the native EcoRI dodecamer. The dodecamer appears symmetric in the NMR spectra and exists largely as an average B-type DNA conformation. However, the H-1 and P-31 NMR spectra give evidence of considerable conformational heterogeneity at the mismatched nucleotides and their nearest neighbors, which increases with increasing temperature. There is no evidence for a significant population of the syn purine conformation. The imino protons of the mispaired bases G4 and G9 are degenerate, resonate at high field, and exchange readily with solvent. These results indicate that the mispaired bases are only weakly hydrogen-bonded and are only partially stacked into the helix. On raising the temperature, the duplex shows increasing exchange between two or more conformations originating from the mismatch sites. However, these additional conformations maintain their Watson-Crick hydrogen bonding. The increase in chemical exchange is consistent with a quasimelting process for which the G.G sites provide local nuclei. Extensive modeling studies by dynamic annealing have confirmed that the G(anti)-G(anti) conformation is favored and that the mispairs are poorly stacked within the helix. The results explain both the poor thermal stability and low hypochromicity of this duplex.