Ringquist S, Smith C L
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder 80309.
Proc Natl Acad Sci U S A. 1992 May 15;89(10):4539-43. doi: 10.1073/pnas.89.10.4539.
The Escherichia coli chromosome encodes two methylases, dam and dcm, which recognize the sequences GATC and CC(A/T)GG, respectively. Specific dam and dcm sites on the E. coli chromosome were found to be unmethylated in vivo by using pulsed-filed gel electrophoresis experiments scanning megabase regions of DNA. Some sites were totally unmethylated. The dam sites display variable methylation depending on the local sequence, and, in general, their methylation shows complex modulation by growth conditions and growth rate, suggesting multiple protection mechanisms. Sites resistant to complete dam or dcm methylation appear to be distributed throughout the chromosome. These unusual sites may identify regions of the chromosome with interesting biological functions.
大肠杆菌染色体编码两种甲基化酶，即dam和dcm，它们分别识别序列GATC和CC(A/T)GG。通过使用扫描兆碱基DNA区域的脉冲场凝胶电泳实验，发现大肠杆菌染色体上特定的dam和dcm位点在体内未被甲基化。一些位点完全未被甲基化。dam位点的甲基化取决于局部序列，并且一般来说，它们的甲基化表现出受生长条件和生长速率的复杂调控，这表明存在多种保护机制。对完全dam或dcm甲基化具有抗性的位点似乎分布于整个染色体。这些不同寻常的位点可能标识出具有有趣生物学功能的染色体区域。
