Tumour-specific phenylalanine tRNA contains two supernumerary methylated bases

Every malignant tumour examined contains aberrant tRNA methyltransferases and a few tRNAs which are absent from the normal tissue of origin. To determine whether tumour-specific tRNAs have different modifications from those in normal tissue, we purified the most frequently occurring tumour-specific isoaccepting tRNA from two malignant tissues. The isoaccepting phenylalanine tRNA from Novikoff hepatoma and Ehrlich ascites cells both contain two supernumerary methylated bases. One of these l-methylguanine, is absent from the phenylalanine tRNA of normal rat, mouse, rabbit and calf liver. An increase in the levels of 5-methylcytidine and dihydrouridine was also detected.