Boehm T L, Drahovsky D
Carcinogenesis. 1981;2(1):39-42. doi: 10.1093/carcin/2.1.39.
Human Raji lymphoblast-like cells were propagated in the presence of various concentrations of N-methyl-N-nitrosourea (MNU) and the degree of enzymatic methylation of newly synthesized DNA was analysed by two independent methods. The overall extent of enzymatic DNA methylation was measured on the basis of [14C]deoxycytidine derived radioactivity incorporated into DNA 5-methylcytosine and cytosine residues. Enzymatic methylation of internal cytosines at 5'-CCGG-3' sequences of Raji DNA was analysed by use of the bacterial restriction enzyme HpaII and its isoschizomer MspI. The data obtained by both methods indicate that the treatment with MNU causes a lower level of enzymatic methylation of newly synthesized DNA. This lower extent of DNA methylation persists in the absence of the carcinogen in the cell cycles following the treatment.
人Raji淋巴母细胞样细胞在不同浓度的N-甲基-N-亚硝基脲（MNU）存在下进行增殖，并通过两种独立方法分析新合成DNA的酶促甲基化程度。基于掺入DNA 5-甲基胞嘧啶和胞嘧啶残基中的[14C]脱氧胞苷衍生放射性来测量酶促DNA甲基化的总体程度。通过使用细菌限制性内切酶HpaII及其同裂酶MspI分析Raji DNA 5'-CCGG-3'序列处内部胞嘧啶的酶促甲基化。两种方法获得的数据表明，MNU处理导致新合成DNA的酶促甲基化水平降低。在处理后的细胞周期中，即使不存在致癌物，这种较低程度的DNA甲基化仍会持续存在。
