Lys-tRNA4 and cell division. Changes in lys-tRNA during the growth of mouse L cells

Methionine sulfoximine in vivo modifies the tRNALys pool of developing rat brain

tRNA was extracted from brains of 3-, 8-, and 18-day-old rats that were injected intracerebrally, 45 min before death, with [3H]methyl methionine or [8-3H]guanosine, and intraperitoneally, 3 h before death, with L-methionine-dl-sulfoximine (MSO), a methylation-activating convulsant agent. Although there was no effect of age or of MSO on the per gram yield of tRNA, its specific radioactivity (dpm/A260) was highest at 3 days in both the control and the MSO groups. Age- and MSO-related changes in tRNALys content of the brain tRNA pool were investigated by means of benzoylated DEAE-cellulose (BDC) and reverse-phase chromatography (RPC). BDC chromatography revealed tRNALys species in the brains of the MSO-treated animals that were absent in control brains. Of particular interest was the finding that differences in RPC-5 chromatographic mobility between control and MSO-tRNALys species were abolished by conversion of lysyl-tRNA, suggesting that the MSO-elicited change(s) in tRNALys structure involved the binding site(s) for lysine. Two additional findings were made: (a) lysine acceptance by the [3H]methyl-labeled tRNALys purified from brains of the MSO-treated animals was higher than that of controls at 18 days; and (b) omission of the BDC chromatographic step accentuated the differences in mobility on RPC-5 columns between tRNALys species of control and MSO-treated animals. Lastly, we found that some tRNALys species of control and MSO-treated brains contained significantly different proportions of N2-methyl guanine and 1-methyl adenine, relative to controls. These MSO-elicited changes in the methyl base content of tRNALys of immature rat brain are the first evidence of an alteration of brain tRNA structure by a centrally acting excitatory agent.

Codon binding and translational properties of an isoaccepting lysine tRNA peculiar to virus-transformed Cells

Isoaccepting lysyl-tRNAs from virus-transformed cells in culture were fractionated in the RPC-5 system into peaks 1, 2, 4, 5a, 5, and 6. tRNALys6 previously was found predominantly associated with transformed cells. The codon response of each peak was determined in an E. coli ribosomal binding assay. tRNALys1, tRNALys2, and tRNALys4 are highly specific for the 5'AAG3' codon. tRNALys5 and tRNALys5a preferentially bind in response to AAA. tRNALys6 binds in response to AAA 3-fold better than in response to AAG. The presence of thiolated nucleosides in the anticodon regions of tRNALys5a, tRNALys5, and tRNALys6 is indicated by I2-inactivation of aminoacylation ability with no effect on the other is isoacceptors. Functional abilities of the isoacceptors were compared in a wheat germ translational system with tobacco mosaic virus RNA as messenger. All of the isoacceptors function about equally well in translation except for tRNALys6, which is only 14 to 24% as effective as the other isoacceptors.

The evolving tRNA molecule

The study of tRNA molecular evolution is crucial to understanding the origin and establishment of the genetic code as well as the differentiation and refinement of the machinery of protein synthesis in prokaryotes, eukaryotes, organelles, and phage systems. The small size of the molecule and its critical involvement in a multiplicity of roles distinguish its study from classical protein molecular evolution with respect to goals and methods. Here, the authors assess available and missing data, existing and needed methodology, and the impact of tRNA studies on current theories both of genetic code evolution and of the evolution of species. They analyze mutational "hot spots", the role of base modification, synthetase recognition, codon-anticodon interactions and the status of organelle tRNA.