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"Silent" mutations are not always silent
A mutation in a human gene that does not change the resulting amino acid can nevertheless change a protein's function, according to an online report from Science. The research marks the first time that the phenomenon has been confirmed in mammals. ..."The habit we all have of disregarding nucleotide changes that don't change protein sequence may not be a good one," coauthor Michael Gottesman at the National Cancer Institute in Bethesda, Md., told The Scientist. "This may be a generalizable phenomenon that may lead to changes in function we haven't been thinking about." ...The idea that synonymous mutations might lead to differently folded proteins was proposed by Ian Purvis at the University of Glasgow and his colleagues and, independently, by Anton Komar, now at Cleveland State University in Ohio.
"Many cases of silent SNPs and their possible link to diseases should be reexamined," Komar, who did not participate in this study, told The Scientist. "Also, one should be quite careful in constructing artificial genes for the purposes of gene therapy, for example, and pay careful attention to the choice of synonymous codons."
Gottesman and his colleagues speculate that synonymous mutations represent rare codons for which translation machinery is not optimized. The resulting interruption of the rate at which mRNAs are translated could affect how a protein is folded, they said. Recent experiments in prokaryotes suggest codon usage is not random. ...Sadee suggested experiments that measure translation rates in vitro might help. He added that recent work of his own suggests that C3435T might affect mRNA folding, which in turn might affect mRNA translation rate and subsequent protein folding.