The regulation of RNA synthesis in yeast. V. tRNA charging studies.

The stringent control of RNA synthesis in the yeast Saccharomyces cerevisiae may be evoked either by starving for a required amino acid or by inhibiting protein synthesis. The response is non-coordinate in that the synthesis of ribosomal and messenger RNA is depressed whereas that of transfer RNA continues. If protein synthesis is blocked in starved cells then tRNA synthesis is stimulated. In this paper, the relationship between the level of tRNA charging and the transcriptional and translational state of the yeast cell has been examined. When cells are starved for an amino acid the corresponding tRNA species only becomes uncharged. This effect can be counteracted by the addition of protein synthesis inhibitors to the starved cells. In contrast, the same inhibitors provoked the discharge of tRNA in growing (non-starved) yeast. Similar results were obtained when protein synthesis was blocked using a temperature-sensitive mutant. These contrasting effects of translation inhibition on tRNA charging in starved and non-starved cells correlate with the changes that inhibition evoked in the transcriptional state of those cells. The data indicate that tRNA synthesis is under autoregulatory control and that tRNA charging may also play an important role in the regulation of rRNA synthesis.