Transfer RNA Base Composition Studies in Morris Hepatomas and Rat Liver

The major and modified base composition of cytoplasmic tRNA from Morris hepatomas 7777 and 5123D and from rat liver has been determined for 16 constituents using a new chemical tritium derivative method. Analysis of the total base composition of the tumor tRNA's did not reveal a general overmodification or overmethylation, but the total modified and methylated base content was found to be slightly lower than in tRNA from normal liver and host liver. As shown by analysis of the modified base composition, hepatoma 7777 tRNA contains less 5-methyluridine, pseudouridine, 3-methylcytidine, and 5-methylcytidine and more dihydrouridine and 1-methylguanosine than does liver, and hepatoma 5123D contains less dihydrouridine and 5-methylcytidine and more N 2, N 2-dimethylguanosine and X (an unidentified modified nucleoside) than does liver. Differences ranged from 2 to 17%, N 2, N 2-dimethylguanosine and X showing the greatest deviations in hepatoma 5123D. For the major nucleosides, differences of 2 to 4% were observed. Both tumor RNA's contain more uridine and less cytidine, and hepatoma 7777 has in addition less adenosine and more guanosine. No unusual modified bases were detected in these tumors by the chromatographic procedures used. A comparison of the two tumor tRNA's does not provide evidence for a distinct correlation between degrees of modification and methylation of tRNA and growth rates and histological characteristics of the tumors. The following possibilities exist for explaining the observed base composition differences: ( a ) changes in concentrations of specific tRNA's; ( b ) presence in the tumors of tRNA's with altered sequences; and ( c ) aberrant modification.