METHYLATION OF TRANSFER-RNA

The methylation of tRNA is a post-transcriptional modification which is achieved by specific enzymes, the tRNA methylases, with S-adenosylmethionine as a methyl donor. The level and pattern of methylation are characteristic of the tRNA species and origin. Abnormally methylated tRNAs were obtained, in vivo and in vitro, by a variety of methods, and their properties were studied. The tRNA methylases are found in all cells and tissues. Their activity varies with the differentiation state of the cells, and under the influence of many internal and external factors; it is especially elevated in embryonic and cancerous tissues. These enzymes are very unstable, and none have been purified to homogeneity. Their known properties are presented and a theory is proposed concerning their specificity. The available experimental data are reviewed, and the current hypotheses and speculations about the roles and functions of tRNA methylation are discussed.