Composition, Associated Tissue Methyltransferase Activity, and Catabolic End Products of Transfer RNA from Carcinogen-induced Hepatoma and Normal Monkey Livers

This investigation was designed to explore transfer RNA tRNA) methyltransferase activity, urinary excretion levels of RNA degradation products, and tRNA base composition in normal monkeys and in those with hepatocellular carcino-nas induced by N-nitrosodiethylamine. After the develop-nent of the tumor, 24-hr urine specimens were collected, he monkeys were sacrificed, and the livers were removed or tRNA Isolation and methyltransferase activity studies. The tRNA methyltransferase activity and capacity and the urinary excretion levels for selected tRNA degradation products (pseudouridine, N²,N²-dimethylguanosine, 1-nethylinosine, 7-methylguanine, and /3-aminoisobutyric icid) were elevated for the hepatoma-bearing monkeys vhen compared to those with normal liver. The isolated RNA pools were analyzed by high-resolution liquid chronatography, and similar base compositions were found for he hepatoma-bearing and normal monkeys. With the use of nethyl-deficient Escherichia coli tRNA as the methyl recepor and the analytical procedure for tRNA analysis, the nethylating ability of the tRNA methyltransferases in hepaoma and normal liver extracts was determined. The hepaoma methyltransferase homogenates were found to pro-luce increased levels of 7-methylguanine, N²,N²-dimethyljuanine, and thymine, while the normal liver extracts gave ligher levels of N²-methylguanine. These differences were lot apparent in the base composition of the tRNA pools, the increased urinary excretion and higher methyltransfertse activity of the hepatoma-bearing monkeys without an apparent increase in the methylated base content of their RNA suggest increased tRNA turnover. However, subtle changes in the methylated base content of individual isoaccepting tRNA's would be missed by analyzing the tRNA pools. The variations in the individual tRNA methyltransferise activities of the hepatoma and normal liver homogelates indicate a difference in the methylation of their RNA's.