Growth-rate-dependent accumulation of twelve tRNA species in Escherichia coli

We have previously shown that in Escherichia coli the accumulation of five leucine and three methionine tRNA species is regulated so that those tRNA species that translate major codons increase while those that translate minor codons decrease as the growth rate increases. Here, we have analyzed the growth-rate-dependence of another 12 tRNA species. We find that the level of three tRNA species cognate to the major glycine, proline and arginine codons, respectively, increase with increasing growth rates. Conversely, four tRNAs that are cognate to minor codons within the same amino acid families decrease with increasing growth rates. In addition, the glutamyl as well as the phenylalanyl isoacceptor species are accumulated in proportion to the content of these two amino acids in the proteins produced at different growth rates. In summary, the patterns of the growth-rate-dependence for the accumulation of these 17 tRNA species support the interpretation that the major codon preference is an arrangement to maximize the growth rates of bacteria in rich media by optimizing the kinetic efficiency of translation. In contrast, we find that three minor tRNA species cognate to two rare arginine codons and one minor glycine codon, respectively, increase with increasing growth rate. Such findings suggest that there are additional constraints on the accumulation of these tRNA species that may be distinct from those required to optimize the kinetic efficiency of translation.