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The First Codon and Its Descendants

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Science  17 Jul 1998:
Vol. 281, Issue 5375, pp. 330
DOI: 10.1126/science.281.5375.330

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Summary

A biophysicist looked for common features in messenger RNA molecules to determine which of the genetic code's "words," or codons--the triplets of bases that code for amino acids--came first. He concludes that the first word was GCU (guanine, cytosine, and uracil) and calculates how GCU might have evolved into the current set of 61 codons that specify the 20 amino acids.