title: Differences in the patterns of methylation in rat liver ribosomal ribonucleic acid after reaction in vivo with methyl methanesulphonate and NN-dimethylnitrosamine.
abstract: 1. rRNA was isolated from rat liver at short intervals after the intraperitoneal injection of [(14)C]methyl methanesulphonate (50mg/kg) or NN-di[(14)C]methylnitrosamine (2mg/kg). These doses were chosen to minimize the effects of toxicity. 2. The following methods of hydrolysis of [(14)C]methylated rRNA were employed: enzymic digestion to nucleosides at pH8; alkaline hydrolysis and conversion into nucleosides; acid hydrolysis to bases. 3. The methylation products were analysed by chromatography on columns of Dowex-50 (H(+) form) and Dowex-50 (NH(4) (+) form). 4. With both methylating agents the principal product of methylation was 7-methylguanine. Differences were obtained, however, in the molar proportions of the minor bases 3-methylcytosine, 1-methyladenine and 7-methyladenine. Methylation at the O-6 position of guanine was a significant feature of rRNA obtained from the NN-di[(14)C]methylnitrosamine-treated animals but was not detected in rRNA after treatment with [(14)C]methyl methanesulphonate.
mesh_terms: D000225:Adenine / Q000032:analysis; D000473:Alkanes / Q000494:pharmacology; D000477:Alkylating Agents / Q000494:pharmacology*; D000818:Animals; D002247:Carbon Isotopes; D002852:Chromatography, Ion Exchange; D003596:Cytosine / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel; D006147:Guanine / Q000032:analysis; D006868:Hydrolysis; D008099:Liver / Q000032:analysis / Q000187:drug effects*; D008745:Methylation; D009602:Nitrosamines / Q000494:pharmacology*; D010727:Phosphoric Diester Hydrolases; D012335:RNA, Ribosomal / Q000032:analysis*; D051381:Rats; D012260:Ribonucleases; D013451:Sulfonic Acids / Q000494:pharmacology
chemical_list: D000473:Alkanes; D000477:Alkylating Agents; D002247:Carbon Isotopes; D009602:Nitrosamines; D012335:RNA, Ribosomal; D013451:Sulfonic Acids; D006147:Guanine; D003596:Cytosine; D012260:Ribonucleases; D010727:Phosphoric Diester Hydrolases; D000225:Adenine