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The Methylation of Transfer RNA in Vitro by Extracts of Normal and Malignant Tissue

Department of Biochemistry, The University of Glasgow, Glasgow, W.2., Scotland

The transfer RNA (tRNA) methylase activities of normal and regenerating rat liver, liver of newborn rats, and a minimum deviation hepatoma have been studied in vitro with Escherichia coli tRNA as substrate. The levels of activity are higher in extracts of malignant, newborn, and regenerating tissue than in extracts of normal tissue, when comparison is made at the optimum concentration of ammonium ions. With liver tRNA as substrate there is no incorporation of methyl groups by the various liver extracts, but a small amount of incorporation was consistently observed under the action of the ethionine tumor extracts.

Sequential incubation of tRNA with extracts from different tissues showed that the ethionine tumor preparation can effect supermethylation of samples previously exposed to enzymes from liver. The reverse experiment gave no incorporation. The addition of tumor enzyme preparation to an assay mixture previously saturated with respect to liver enzyme can bring about an increase in the extent of methylation of E. coli tRNA. These observations suggest that there are some differences in the complement of tRNA methylases in the malignant tissue compared with the normal.

¹ Present address: Department of Clinical Chemistry, Royal Infirmary, Dundee, Scotland.

Received 1/ 2/69. Accepted 5/ 2/69.