A transplantable rat
tumor, mammary
adenocarcinoma 13762, accumulates
tRNA which can be methylated in vitro by mammalian
tRNA (adenine-1)
methyltransferase. This unusual ability of the
tumor RNA to serve as substrate for a homologous
tRNA methylating
enzyme is correlated with unusually low levels of the A 58-specific adenine-1
methyltransferase. The nature of the methyl-accepting
RNA has been examined by separating
tumor tRNA on two-dimensional
polyacrylamide gels. Comparisons of
ethidium bromide-stained
gels of
tumor vs. liver
tRNA show no significant quantitative differences and no accumulation of novel tRNAs or precursor tRNAs in
adenocarcinoma RNA. Two-dimensional separations of
tumor RNA after in vitro [14C]methylation using purified adenine-1
methyltransferase indicate that about 25% of the
tRNA species are strongly methyl-accepting RNAs. Identification of six of the tRNAs separated on two-dimensional
gels has been carried out by hybridization of cloned
tRNA genes to Northern blots. Three of these, tRNALys3 ,
tRNAGln and tRNAMeti , are among the
adenocarcinoma methyl-accepting RNAs. The other three RNAs, all of which are
leucine-specific tRNAs, show no methyl-accepting properties. Our results suggest that low levels of a
tRNA methyltransferase in the
adenocarcinoma cause selected species of
tRNA to escape the normal A58 methylation, resulting in the appearance of several mature tRNAs which are deficient in
1-methyladenine. The methyl-accepting tRNAs from the
tumor appear as
ethidium bromide-stained spots of similar intensity to those seen for
RNA from rat liver; therefore, methyladenine deficiency does not seem to impair processing of these tRNAs.