Biological and structural differences between tRNAVal species isolated from rat ascites hepatoma cells and normal rat...

On RPC-5 column chromatography, the main valine acceptor activity of tRNA (tRNA2Val) from rat ascites hepatoma cells was eluted later than that of normal rat liver tRNA (tRNA1Val). The tRNA2Val was aminoacylated by E. coli amino-acyl-tRNA synthetase, while tRNA1Val from normal rat liver was not. Rat fetal liver tRNAVal was also aminoacylated by E. coli aminoacyl-tRNA synthetase. tRNA1Val (rat liver) and tRNA2Val (ascites hepatoma) were each purified to a homogeneous state by RPC-5 column chromatography and two-dimensional polyacrylamide gel electrophoresis, and their sequences were determined by post-labeling techniques. Ascites hepatoma tRNA2Val differed from rat liver tRNA1Val in that Gm18, C32 and an unknown modified nucleoside, N34, in the latter tRNA were mostly replaced by G, Cm, and inosine, respectively. In addition, 3'-terminal adenosine was not present in tRNA1Val (normal rat liver), but was in tRNA2Val (ascites hepatoma). Other modifications and the primary structures of the two tRNAValS were found to be the same. Thus it was concluded that the new iso-acceptor species of tRNA Val in ascites hepatoma cells is due to a change of post-transcriptional modification, not to a change of tRNA transcription. The unique feature of the change of post-transcriptional modification in tRNA2Val (ascites hepatoma) is that both hypo- and hyper-modification take place simultaneously in the tRNA molecule depending the locations of nucleotide residues.