Groudine M, Eisenman R, Weintraub H
Nature. 1981 Jul 23;292(5821):311-7. doi: 10.1038/292311a0.
The transcriptionally active ev-3 and inactive ev-1 endogenous retrovirus loci in chick cells differ in that ev-3 is undermethylated, preferentially sensitive to DNase I digestion, and contains nuclease hypersensitive sites in each of its two long terminal repeats. Transient exposure of cells to 5-azacytidine, a cytosine analogue which cannot be methylated at the 5 position, results in the hypomethylation and transcriptional activation of ev-1, as well as the acquisition of at least one nuclease-hypersensitive site within the chromosomal domain of ev-1.
鸡细胞中转录活跃的ev-3和无转录活性的ev-1内源性逆转录病毒基因座的差异在于，ev-3处于低甲基化状态，对DNA酶I消化具有优先敏感性，并且在其两个长末端重复序列的每一个中都含有核酸酶超敏位点。细胞短暂暴露于5-氮杂胞苷（一种在5位不能甲基化的胞嘧啶类似物）会导致ev-1的低甲基化和转录激活，以及在ev-1的染色体区域内获得至少一个核酸酶超敏位点。
