Mature methyl-deficient tRNA isolated from a mammary adenocarcinoma.
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.
D000230:Adenocarcinoma / Q000201:enzymology*; D000818:Animals; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D005260:Female; D008099:Liver / Q000032:analysis; D008325:Mammary Neoplasms, Experimental / Q000201:enzymology*; D008745:Methylation; D051381:Rats; D011916:Rats, Inbred F344; D014316:Tritium; D012359:tRNA Methyltransferases / Q000172:deficiency* / Q000378:metabolism
D014316:Tritium; D012359:tRNA Methyltransferases; C023194:tRNA (adenine(58)-N(1))-methyltransferase