It turns out that there is a reason for this redundancy. Some codons are faster and easier for cells to process and assemble into proteins than others. Recognition of this difference led to the concept of optimal codons and the hypothesis that natural selection should drive organisms particularly fast growing ones to use genes that use optimal codons to make critical proteins that need to be highly abundant or synthesized rapidly in cells.
The problem with this hypothesis was shown by Johnson and Rokas' study of the effect of changing codon usage on the simple biological clock found in single-celled cyanobacteria (blue-green algae) and a similar study of the more complex biological clock found in bread mold performed by a team led by Yi Liu that were published together.
"What the Liu team found was that optimizing all the codons used by the fungal biological clock knocked the clock out, which was totally unexpected! Those researchers concluded that clock proteins in the fungus are not properly assembled if they are synthesized too rapidly; it's as if the speed of one's writing affected our ability to read the text," Johnson summarized.
In the cyanobacteria, however, the researchers observed a different phenomenon. At Vanderbilt, Research Associate Professor Yao Xu optimized the codons in the cyanobacteria's biological clock. This did not shut the cloc
|Contact: David Salisbury|