Premium
The ‘polysemous’ codon—a codon with multiple amino acid assignment caused by dual specificity of tRNA identity
Author(s) -
Suzuki Tsutomu,
Ueda Takuya,
Watanabe Kimitsuna
Publication year - 1997
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/16.5.1122
Subject(s) - biology , transfer rna , genetics , amino acid , stop codon , dual (grammatical number) , identity (music) , computational biology , rna , gene , linguistics , physics , acoustics , philosophy
In some Candida species, the universal CUG leucine codon is translated as serine. However, in most cases, the serine tRNAs responsible for this non‐universal decoding (tRNA Ser CAG) accept in vitro not only serine, but also, to some extent, leucine. Nucleotide replacement experiments indicated that m 1 G37 is critical for leucylation activity. This finding was supported by the fact that the tRNA Ser CAGs possessing the leucylation activity always have m 1 G37, whereas that of Candida cylindracea , which possesses no leucylation activity, has A37. Quantification of defined aminoacetylated tRNAs in cells demonstrated that 3% of the tRNA Ser CAGs possessing m 1 G37 were, in fact, charged with leucine in vivo . A genetic approach using an auxotroph mutant of C.maltosa possessing this type of tRNA Ser CAG also suggested that the URA3 gene inactivated due to the translation of CUG as serine was rescued by a slight incorporation of leucine into the polypeptide, which demonstrated that the tRNA charged with multiple amino acids could participate in the translation. These findings provide the first evidence that two distinct amino acids are assigned by a single codon, which occurs naturally in the translation process of certain Candida species. We term this novel type of codon a ‘polysemous codon’.