Methylation of DNAase-digestible DNA and of RNA in chromatin from rats treated with dimethylnitrosamine.
After injecting rats with di[14C]methylnitrosamine we have prepared liver chromatin and have examined firstly, the methylation level of the DNAase I-degradable fraction of the DNA and secondly, the level of methylation and the stability of methylated sites in chromatin RNA. Our results show that the level of 7-methylguanine in the degradable DNA is about 1.3 times that of whole DNA; therefore in the 20% or so of the DNA which is undegradable by DNAase I, the level must be very low or zero. Experiments using chromatin from rats injected with unlabelled dimethylnitrosamine plus [3H]thymidine show that the specific activity is similar in the DNAase I degradable and undegradable fractions, suggesting that there is no preferential repair in the latter region. In chromatin RNA, the level of 7-methylguanine is higher than that of whole DNA and decreases fairly rapidly within 30 h after dimethylnitrosamine treatment. Our results indicate that this decrease is due to some type of excision or repair process rather than to normal turnover.
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D003851:Deoxyribonucleases; D004128:Dimethylnitrosamine / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D008745:Methylation; D009602:Nitrosamines / Q000378:metabolism*; D012313:RNA / Q000378:metabolism*; D051381:Rats
D002843:Chromatin; D009602:Nitrosamines; D012313:RNA; D004247:DNA; D003851:Deoxyribonucleases; D004128:Dimethylnitrosamine