In order to elucidate the effects of cytosine methylation on deoxyribonucleic acid (DNA) conformation, three self-complementary deoxyribodecanucleotides, d(ATACGCGTAT), d(ATACGm5CGTAT) and d(ATAm5CGm5 CGTAT), were synthesized by a modified phosphotriester method and their conformational properties were examined by ultraviolet (UV) and circular dichroism (CD) spectroscopy. The two modified decamers were completely resistant to restriction endonuclease MluI, whose recognition sequence is ACGCGT, while the unmodified decamer was completely cleaved by the enzyme. All the decamers were assumed to exist as a B-form duplex in 0.1 M NaCl. The UV-temperature profiles suggested that the modified decamer duplexes have slightly higher stability to thermal perturbation but their melting processes are significantly less cooperative, as compared to the case of the unmodified decamer. All three decamers showed similar CD spectra under various salt conditions, including 4M NaCl and 6M CsF. However, substantial differences in CD spectra were observed in 8M NaClO4 at -20°C. Both modified decamers were assumed to exist as a Z-form duplex under these extreme conditions, and they showed similar UV and CD-temperature profiles which were quite different from those of the unmodified decamer.
为了阐明
胞嘧啶甲基化对
脱氧核糖核酸(DNA)构象的影响,我们采用改进的
磷酸酯法合成了三种自互补的脱氧
核糖核苷酸,即d(ATACGCGTAT)、d(ATACGm5CGTAT)和d(ATAm5CGm5 CGTAT),并通过紫外光谱(UV)和圆二色光谱(CD)研究了它们的构象特性。两种修饰的十聚体对限制性内切酶 MluI(其识别序列为 ACGCGT)具有完全的抗性,而未修饰的十聚体则完全被该酶裂解。假定所有十聚体在 0.1 M NaCl 中都以 B 型双链存在。紫外-温度曲线表明,与未修饰的十聚体相比,修饰的十聚体双链对热扰动的稳定性略高,但其熔化过程的协同性明显较低。在各种盐条件下,包括 4M NaCl 和 6M CsF,所有三种十聚体都显示出相似的 CD 光谱,但在 -20°C 下的 8M NaClO4 中观察到的 CD 光谱有很大差异。在这些极端条件下,两种修饰的十聚体都被假定为 Z 形双链体,它们显示出相似的紫外光谱和 CD 温度曲线,与未修饰十聚体的曲线截然不同。