In chloroplasts, all 61 sense codons are found in chloroplast (cp) DNA sequences coding for proteins. However among the sequenced cp tRNAs or tRNA genes, tRNAs with anticodons complementary to codons CUU/C (Leu), CCU/C (Pro), GCU/C (Ala) and CGC/A/G (Arg) [or CGC/A (Arg) in Marchantia] have not been found. In this paper we show that cp tRNA(Ala)(U*GC) cp tRNA(Pro)(U*GG) and cp tRNA(Arg)(ICG) are able to decode the corresponding four-codon family. In the case of leucine codons CUU/C, we show that 'U:U and U:C wobble' mechanisms can operate to allow the reading of these codons by cp tRNA(Leu)(UAm7G).

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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.

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