Figure 2.

Expression levels of protein and RNAs. (A) Analysis of wild-type and mutant AspRS and mRNA^AspRS expressions in yeast strains without (−) or with (+) plasmids encompassing an extra tRNA^Asp gene (in the (−) strains, the tRNA^Asp gene was replaced by a tRNA^Ile gene). Controls (c) correspond to nontransformed cells. (B) mRNA^AspRS and tRNA^Asp expression under the control of heterologous promoters. AspRS genes (wild type or mutated) were cloned under the control of the glyceraldehyde-3 phosphate dehydrogenase (GPD) promoter (strong constitutive promoter) or the Gal 1 promoter (strong inducible promoter) and the level of mRNA^AspRS expression was determined in the presence of different tRNA^Asp concentrations. No results were obtained with the mutated AspRS expressed under the GPD promoter, because the transformed yeast strains cannot grow properly. Quantitative data are given, representing mean values (about ±20%) of two independent experiments; values were calculated as a ratio of AspRS or mRNA^AspRS or tRNA^Asp with respect to controls and normalized towards the internal calibration controls (glucose 6-phosphate dehydrogenase (G6PDH), the mRNA encoding β-actin and 5S rRNA, respectively).