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Increase of Soluble RNA¹ Methylase Activities by Chemical Carcinogens^,2

Division of Medical Biochemistry, Faculty of Medicine, The University of Calgary, Calgary T2N 1N4, Alberta, Canada

High levels of the hepatocarcinogen ethionine (1% of the DL isomer mixture) in diets were shown to increase soluble RNA methylase activity of rat and hamster liver cells. Enzyme increases were detected after only 4 days of ethionine feeding. Dimethylaminoazobenzene, another hepatocarcinogen, also increased soluble RNA methylase activity. Noncarcinogenic analogs of ethionine, norleucine and L-methionine, did not cause this increase in activity. Liver enzyme preparations from ethionine-treated rats methylated yeast phenylalanine transfer RNA more extensively than did enzymes from normal liver. The only nucleotides methylated were uridylic acid and cytidylic acid with the latter being 6 times more methylated. Ethionine treatment did not alter the amounts of soluble RNA methylase inhibitors. The same ethionine enhancement of soluble RNA methylase activity could be demonstrated in metabolizing yeast cells.

¹ Make a distinction between "sRNA", or that RNA which is obtained from the soluble portion of the cell, and "tRNA," which is partially or wholly purified (resolved) tRNA's.

² This investigation was supported by Grant MA 4126 from the Medical Research Council of Canada.

Received 8/24/72. Accepted 4/ 5/73.