Molecular Biology

Ambiguous Dogma

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Science  25 Jun 2004:
Vol. 304, Issue 5679, pp. 1879
DOI: 10.1126/science.304.5679.1879a

In modern organisms, each amino acid in a protein is encoded by a triplet codon. The triplet code is unambiguous (AUA and AUU always encode isoleucine, for example) as is the amino acid sequence of a protein, a feature assumed to be important to its function. But this one-to-one mapping may not always have been so: During early evolution, amino acids may have been assigned to more than one codon. Such an imprecise code would result in “statistical” proteins, where at any particular position, any one of several amino acids could be found.

Pezo et al. have generated bacteria with a mutation in the editing function of isoleucine transfer RNA synthetase, which results in the incorporation of a range of related amino acids at positions specified by isoleucine codons. Such proteins are not intrinsically detrimental to growth or health. Indeed, under conditions of limiting isoleucine availability, they have a distinct advantage compared to wild-type bacteria, as they are able to incorporate other, non- limiting amino acids. The authors speculate that statistical coding may have been an advantage in early environments, maximizing the utility of available resources. — GR

Proc. Natl. Acad. Sci. U.S.A. 101, 8593 (2004).

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