Adjustment of the tRNA population to the codon usage in chloroplasts

Abstract

In chloroplasts there is a correlation between the amounts of tRNAs specific for a given amino acid and the codons specifying this amino acid. Furthermore, for the amino acids coded for by more than one codon, the population of isoaccepting tRNAs is adjusted to the frequency of synonymous codons used in chloroplast protein genes. A comparison by two-dimensional gel electrophoresis of the tRNA populations extracted from chloroplasts and from chloroplast polysomes shows that all chloroplast tRNAs are involved in protein biosynthesis.

On the Evolution and Expression of Chlamydomonas reinhardtii Nucleus-Encoded Transfer RNA Genes

“…This mechanism of coadaptation between tRNA gene number and codon usage seems to be frequent and has already been reported in different organisms such as E. coli and C. elegans (Bulmer 1987;Duret 2000). Furthermore, hybridization of pCp-labeled total tRNAs from C. reinhardtii with oligonucleotides specific to different tRNA isoacceptors permitted us to show that indeed for the studied tRNAs (Figure 4) In various organisms and chloroplasts, the abundance of specific tRNAs was shown to be directly correlated to the frequency of the cognate codons (Pfitzinger et al 1987;Dong et al 1996). Here, in Chlamydomonas, in relation to the number of the corresponding genes, it seems that there is also a good adjustment of the tRNA population to the cytosolic codon usage.…”

“…There is only one exception to this rule, the case of initiator AUG methionine codons where the number of genes is far higher than expected from the abundance of the initiation codon. It is likely that the initiator tRNA Meti has to be abundant to not be a limiting factor in the initiation of translation, as already suggested in chloroplasts (Pfitzinger et al 1987). This mechanism of coadaptation between tRNA gene number and codon usage seems to be frequent and has already been reported in different organisms such as E. coli and C. elegans (Bulmer 1987;Duret 2000).…”

“…Furthermore, there is a codon bias in C. reinhardtii, with some codons highly used in highly expressed genes. In several organisms such as Escherichia coli, yeast, and Caenorhabditis elegans or in chloroplasts, an adjustment of tRNA population to the codon usage exists (Bulmer 1987;Pfitzinger et al 1987;Duret 2000). We therefore asked the question whether a coadaptation between tRNA gene number, tRNA abundance, and codon usage occurs in this green alga.…”

Variations in the Levels of Chloroplast tRNAs and Aminoacyl-tRNA Synthetases in Senescing Leaves of Phaseolus vulgaris

“…In plants, it has been shown that a loss of specific tRNAs occurs in chloroplasts during senescence of leaves (25). Recently, it was shown that in chloroplasts there is a correlation between the amounts of tRNAs specific for a given amino acid and the frequency of the codons specifying this amino acid (16). Furthermore, for the amino acids coded for by more than one codon, the population of isoaccepting tRNAs is adjusted to the frequency of the corresponding synonymous codons.…”

“…Furthermore, for the amino acids coded for by more than one codon, the population of isoaccepting tRNAs is adjusted to the frequency of the corresponding synonymous codons. Such an adjustment is probably necessary to ensure maximum efficiency in chloroplast protein biosynthesis (16). Thus, during senescence, limiting quantities of specific chloroplast tRNAs or aminoacyl-tRNA synthetases could restrict the chloroplast's capacity to read certain codons, and the resulting decrease in synthesis of essential cellular protein components would lead to deleterious effects on cell function.…”