Garcia R A, Bustamante C J, Reich N O
Department of Chemistry, University of California, Santa Barbara 93106, USA.
Proc Natl Acad Sci U S A. 1996 Jul 23;93(15):7618-22. doi: 10.1073/pnas.93.15.7618.
DNA methyltransferases modify specific cytosines and adenines within 2-6 bp recognition sequences. We used scanning force microscopy and gel shift analysis to show that M.HhaI, a cytosine C-5 DNA methyltransferase, causes only a 2 degree bend upon binding its recognition site. Our results are consistent with prior crystallographic analysis showing that the enzyme stabilizes an extrahelical base while leaving the DNA duplex otherwise unperturbed. In contrast, similar analysis of M.EcoRI, an adenine N6 DNA methyltransferase, shows an average bend angle of approximately 52 degrees. This distortion of DNA conformation by M.EcoRI is shown to be important for sequence-specific binding.
DNA甲基转移酶会修饰2至6个碱基对识别序列中的特定胞嘧啶和腺嘌呤。我们利用扫描力显微镜和凝胶迁移分析表明，胞嘧啶C-5 DNA甲基转移酶M.HhaI在结合其识别位点时仅引起2度的弯曲。我们的结果与先前的晶体学分析一致，该分析表明该酶稳定了一个螺旋外碱基，而DNA双链体的其他部分未受干扰。相比之下，腺嘌呤N6 DNA甲基转移酶M.EcoRI的类似分析显示平均弯曲角度约为52度。M.EcoRI对DNA构象的这种扭曲被证明对序列特异性结合很重要。
