Amino acids are used approximately in proportion to cognate tRNA concentrations.

(A) Relative uses of amino acids estimated from the transcriptomic data of 7 model eukaryotes are compared to the relative concentrations of their cognate tRNAs measured from gene copy numbers. The diagonal line shows the predicted proportional relationship between tRNA concentrations and cognate amino acid frequencies that maximizes translational efficiency under tRNA shortage. P_E (or P_M) is the probability that the Euclidian (or Manhattan) distance between the amino acid usage randomly generated under a uniform distribution and that predicted by the proportional rule is smaller than the observed distance, and is estimated from 10⁶ simulations. The distance definitions are the same as those in the legend of Figure 2, except that i is an amino acid instead of a codon. (B) The average CST of an amino acid in S. cerevisiae is negatively correlated with the availability of its cognate tRNAs, which is measured by the fraction of cognate tRNA genes among all tRNA genes divided by the frequency of the amino acid estimated from the transcriptome. The P-value is determined from 1000 permutations of CSTs.