Bergerat A, Kriebardis A, Guschlbauer W
Département de Biologie, Centre d'Etudes Nucléairs de Saclay, Gif-sur-Yvette, France.
J Biol Chem. 1989 Mar 5;264(7):4064-70.
The methylation pattern of the 22 GATC sites of pBR322 (dam-) by Dam methyltransferase from Escherichia coli has been studied. Preferential hemimethylation took place at positions 3042 and 349. It was found that these preferential methylations were the same in supercoiled circular and linear DNAs. The flanking regions of these preferentially methylated sites contain three G.C pairs on one side and two A.T pairs and one G.C pair on the other. This preferential methylation was confirmed on a 126-base pair oligonucleotide containing two GATC sites with different flanking sequences. The next sites methylated were, in both cases, the first GATC site on the A.T-rich side, although the orientation was different. The rapid methylation of a second and third neighboring GATC site on the same plasmid suggests a processive mechanism. The implications of the orientation of hemimethylation are discussed in the context of the recognition of a palindromic target site by a monomeric DNA-binding protein.
对大肠杆菌Dam甲基转移酶作用下pBR322（dam-）的22个GATC位点的甲基化模式进行了研究。在3042和349位点发生了优先半甲基化。结果发现，这些优先甲基化在超螺旋环状DNA和线性DNA中是相同的。这些优先甲基化位点的侧翼区域一侧含有三个G.C碱基对，另一侧含有两个A.T碱基对和一个G.C碱基对。在一个含有两个侧翼序列不同的GATC位点的126个碱基对的寡核苷酸上证实了这种优先甲基化。在这两种情况下，接下来甲基化的位点都是富含A.T一侧的第一个GATC位点，尽管方向不同。同一质粒上第二个和第三个相邻GATC位点的快速甲基化表明存在一种连续作用机制。在单体DNA结合蛋白识别回文靶位点的背景下讨论了半甲基化方向的意义。
