SCIENCE

"Coral reefs aren't just a matter of aesthetics," Oppenheimer said. "Saving coral reefs can be a matter of saving lives."

-- Juliet Eilperin

'Silent' Mutation Not So Silent

According to the classical understanding of how DNA works, if two different genes tell a cell how to make the same protein, then the two proteins produced from those instructions should be interchangeable. Because they have the same chemical structure they should have the same biological function.

A study published online last month by the journal Science provides evidence that the assumption may not always be the case. Sometimes, it seems, "identical" proteins behave differently.

Michael M. Gottesman of the National Cancer Institute and Chava Kimchi-Sarfaty of the Food and Drug Administration report that what should have been a "silent" mutation in a gene involved in making cells drug-resistant was not silent after all.

In the mutant gene, a substitution was made for one of the three letters in the DNA "word," or codon, specifying one of the amino acids in the protein chain. The new letter, however, was synonymous with the original one, which meant the amino acid did not change, and neither did the chemical structure of the final protein. And yet, the scientists reported, the final protein behaved differently.

They believe the explanation for their finding is this:

The codon containing the mutation is harder for the cell to read than the correctly spelled codon. It is translated by the protein-building machinery at a different rate. That slower assembly causes the protein to fold into a slightly different final three-dimensional structure. That different structure, in turn, makes the protein behave differently when it goes to work in the body.

This curious observation may explain why in a few genetic diseases it is sometimes impossible to find a mutation that actually changes the protein's amino acid sequence. Such changes may not be there. It may only be "silent" mutations that are causing the problems.

-- David Brown