Cervi A R, Guy A, Leonard G A, Téoule R, Hunter W N
Department of Chemistry, University of Manchester, UK.
Nucleic Acids Res. 1993 Dec 11;21(24):5623-9. doi: 10.1093/nar/21.24.5623.
The structure of d(CGCGm4CG) were m4C = N4-methylcytosine has been determined by crystallographic methods. The crystals are multifaced prisms, with orthorhombic space group P2(1)2(1)2(1) and unit cell dimensions of a = 17.98, b = 30.77 and c = 44.75A. The asymmetric unit consists of one duplex of hexanucleotide and 49 waters. The R-factor is 0.189 for 1495 reflections with F > or = sigma(F) to a resolution limit of 1.8A. The double helix has a Z-DNA type structure which appears to be intermediate in structure to the two previously characterised structure types for Z-DNA hexamers. The two m4C.G base-pairs adopt structures that are very similar to those of the equivalent base-pairs in the structure of the native sequence d(CGCGCG) except for the presence of the methyl groups which are trans to the N3 atoms of their parent nucleotides and protrude into the solvent region. The introduction of the modified base-pairs into the d(CGCGCG) duplex appears to have a minimal effect on the overall base-pair morphology of the Z-DNA duplex.
已通过晶体学方法确定了d（CGCGm4CG）的结构，其中m4C为N4-甲基胞嘧啶。晶体为多面棱柱体，属于正交晶系空间群P2(1)2(1)2(1)，晶胞参数为a = 17.98、b = 30.77和c = 44.75埃。不对称单元由一个六核苷酸双链体和49个水分子组成。对于1495个F≥σ(F)的反射，在分辨率极限为1.8埃时，R因子为0.189。该双螺旋具有Z-DNA型结构，其结构似乎介于之前表征的两种Z-DNA六聚体结构类型之间。两个m4C.G碱基对所采用的结构与天然序列d（CGCGCG）结构中的等效碱基对非常相似，只是甲基位于其亲本核苷酸N3原子的反位并伸向溶剂区域。将修饰后的碱基对引入d（CGCGCG）双链体似乎对Z-DNA双链体的整体碱基对形态影响最小。
