Waalwijk C, Flavell R A
Nucleic Acids Res. 1978 Dec;5(12):4631-4. doi: 10.1093/nar/5.12.4631.
We have analysed DNA modification in a HapII site (CCGG) present in the major intron of the discontinuous rabbit beta-globin gene. In most somatic tissues, including erythroid and non-erythroid tissues, about 50% of the DNA is resistant to cleavage at this site by HapII, though 100% cleavage is found with the isoschizomer MspI. Since the former enzyme is unable to cleave CCGG sites if the internal C residue is 5-methyl C (and since methylation is the only form of CpG modification documented in animal DNA), while the latter enzyme cleaves DNA irrespective of methylation at this residue, we infer that 50% of the CCGG sites in the beta-globin gene intron are methylated in these tissues. The same site appears to be 100% methylated (judged by the same criterium) in sperm DNA and about 80% methylated in brain DNA. DNA from the rabbit SIRC cell line is entirely unmethylated at this site.
我们分析了不连续的兔β-珠蛋白基因主要内含子中一个HapII位点（CCGG）处的DNA修饰情况。在大多数体细胞组织中，包括红细胞和非红细胞组织，约50%的DNA在该位点对HapII的切割具有抗性，不过同裂酶MspI能实现100%切割。由于如果内部C残基为5-甲基C，前一种酶就无法切割CCGG位点（且由于甲基化是动物DNA中记录的唯一形式的CpG修饰），而后一种酶切割DNA时不考虑该残基处的甲基化情况，我们推断β-珠蛋白基因内含子中50%的CCGG位点在这些组织中发生了甲基化。在精子DNA中，同一位点似乎100%甲基化（依据相同标准判断），在脑DNA中约80%甲基化。兔SIRC细胞系的DNA在该位点完全未甲基化。
