Expanding The Genetic Code | January 12, 2009 Issue - Vol. 87 Issue 2 | Chemical & Engineering News
Volume 87 Issue 2 | p. 38 | Concentrates
Issue Date: January 12, 2009

Expanding The Genetic Code

Some microorganisms surprisingly are able to use one three-nucleic-acid codon to code for more than one type of amino acid
Department: Science & Technology

A basic tenet of translating RNA into protein is that each three-nucleic-acid codon codes for only one amino acid. Not so, says a research group led by Vadim N. Gladyshev of the University of Nebraska, Lincoln. Gladyshev and colleagues have demonstrated that, at least in some microorganisms, the uracil-guanine-adenine (UGA) codon can specify addition of either cysteine or selenocysteine to a growing peptide chain (Science 2009, 323, 259). This variability can show up even between UGA codons specified within a single gene. Working with the gene for thioredoxin reductase 1 from the ciliated protozoan Euplotes crassus, the researchers found that the first six of seven UGA codons in the gene yielded cysteine in the final protein, whereas the seventh UGA codon brought in selenocysteine. The coding difference may lie in the changing condition of a so-called selenocysteine insertion sequence (SECIS) in the gene. The researchers hypothesize that the messenger RNA structure initially buries the SECIS element. Then, as the RNA is translated, the SECIS structure is uncovered and interacts with the translation machinery to insert selenocysteine at the seventh UGA codon.

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