Functionally impaired tRNA from ethionine treated rats as detected in injected Xenopus oocytes.

Treatment of rats with ethionine was found to cause severe impairment in the aminoacylation capacity of tRNA. This effect was only observed when assayed in injected oocytes, while invitro assays of aminoacylation failed to detect differences between normal tRNA and tRNA from ethionine treated animals. The effect of ethionine on the tRNA population was not uniform and differed for various amino acid specific tRNAs. Thus liver tRNA from ethionine treated rats showed a decreased capacity for phenylalanine aminoacylation, while no change was found in the case of leucine. On the other hand, the level of histidine aminoacylation was higher for tRNA from ethionine treated animals. An even more complex response was observed with methionine aminoacylation where tRNA from ethionine treated animals showed an initially faster rate than control tRNA. With more prolonged incubation periods, the methionyl-tRNA from ethionine treated animals was deacylated at an accelerated rate while the level of normal methionyl-tRNA remained almost constant. In addition to the aminoacylation reaction, the participation of aminoacyl-tRNA in protein synthesis was severely impaired. In this case, both the injected oocyte system and the cell-free wheat germ assay revealed these differences which were manifested with various mRNA and viral RNA preparations.