Abstract
The universal genetic code is used in higher plant chloroplasts and all 61 codons are found in protein-coding regions. The 20 common amino acids, except for methionine and tryptophan, are coded for by 2 to 6 synonymous codons. Codon usage of synonymous codons is different by different plants. We have developed an in vitro translation system from tobacco chloroplasts, which allows us to determine translation rates of chloroplast mRNAs. Using this system, we devised an in vitro assay for relative translation rates of synonymous codons. We found that translation efficiencies of synonymous codons are not always correlated with codon usage in tobacco chloroplasts. This raises an important question for the so-called codon optimization according to codon usage.
