Various
tumor cells contain chromatographically distinct isoacceptor
tRNA species. To decide whether the
tumor-specific species represent an expression of a separate
tRNA gene or only an undermodified form of normal
tRNAPhe, nucleotide sequences of
tRNAPhe isolated from
neuroblastoma and normal mouse liver were determined by postlabeling techniques. The results showed identical sequences except for the changes of post-transcriptional modifications in the
anticodon loop. Normal mouse liver
tRNAPhe contained Cm32, Gm34, and the hypermodified YOH next to the 3' end of the
anticodon. On the contrary,
tRNAPhe from
neuroblastoma contained C32, G34, and, instead of YOH base m1G. A small proportion of
tRNAPhe species contained an undermodified YOH base. For the examination of the conditions leading to the undermodified
tRNAPhe, Vero cells derived from the kidney of African green monkey in culture were used. In these cells, deprivation of
methionine or
lysine resulted in changes in
tRNAPhe modification similar to those in
tumor cells.
Ehrlich ascites tumor cells were examined to determine whether the presence of altered
tRNAPhe species in various
tumors is also the result of
starvation of some nutritional factors. Results obtained with these cells showed that
tRNAPhe species lacking the
Y base disappeared in
tumor-bearing mice after
intraperitoneal injection with a mixture of
amino acids and
vitamins. Thus it is concluded that
tumor-specific
tRNAPhe species are the products of aberrant post-transcriptional modification, not the transcripts of different, normally repressed genes.