Extracts prepared from rat kidney and rat kidney tumours catalysed the methylation of unfractionated tRNA from Escherichia coli forming 7 methylated bases; 1-methyladenine, N2-methylguanine, 5-methylcytosine, N2,N2-dimethylguanine, 7-methylguanine, 1-methylguanine and 5-methyluracil. These extracts methylated tRNAfMet forming only 1-methyladenine, N2-methylguanine and 1-methylguanine and tRNAGlu forming 1-methyladenine and 5-methylcytosine. Putrescine, spermidine, Mg2+ and NH4+ stimulated these reactions and the relative activities of these cations in this respect depended on the tRNA added as substrate. The tumour extracts were more active than those from normal kidney but the same spectrum of methylated products was produced with each tRNA substrate by both extracts and there was no evidence of a different specificity of tumour methylases towards the tRNAs used in this study.
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