For more than 8 years, Yves Barral’s group at the ETH in Zürich has puzzled over this question: When the same amino acid is repeated several times in a protein, why is it often specified by the same codon? His group used a combination of biological and computational approaches to show that the transfer RNA (tRNA) adaptor molecules that add the appropriate amino acid to the growing protein hang around the ribosome and can be reused, making translation more efficient.
The genetic code is redundant: up to six codons—each comprised of three nucleotides—can specify just one amino acid. But these so-called “synonymous” codons—specifying the same amino acid—do not occur randomly. This has been “right in front of everyone’s nose,”...
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