A single swap in the letters of a gene's sequence could modify the protein it encodes, even if the switch doesn't change which amino acids make up the molecule, researchers report. The finding could upset a central view in biology—that proteins made of the same amino acids are identical.
DNA contains components called nucleotides, symbolized by the letters A, T, G, and C. Each block of three of these letters—known as a codon—signals a cell's protein-making machinery to add a particular amino acid to a lengthening chain. Most of the 20 amino acids are each encoded by two or more of these three-letter combinations.
Biologists have long held that swapping one codon for another doesn't change the resulting protein's structure, as long as both codons instruct the machinery to insert the same amino acid. However, experiments by Michael Gottesman of the National Cancer Institute in Bethesda, Md., and his colleagues led the team to suspect that those silent mu