``Each gene encodes a protein,`` Hirsh explained. ``By comparing the proteins that yeast and roundworms have in common, we can infer how rapidly their genes evolved.``
He noted that yeast is a particularly good model for evolutionary research - not only because its DNA has been fully mapped, but also because of recent studies showing that many yeast proteins form interacting networks that allow them to communicate with one another inside the cell.
``How genes interact to form complex traits in an organism is a relatively new aspect of evolutionary theory,`` said Stanford biologist Marcus W. Feldman, co-author of the Science study.
He pointed out that yeast - a relatively simple fungus - has 6,000 genes; the roundworm 19,000; and humans, with all of our complexity, only 30,000 to 40,000.
``How do these species accomplish all they do with such a limited number of genes? The answer - protein interactions,`` added Feldman, the Burnet C. and Mildred Finley Wohlford Professor in the School of Humanities and Sciences.
By comparing the amino acid sequences in 2,235 yeast and roundworm proteins, Feldman and his team confirmed a prediction made more than 20 years ago: Proteins that interact with a large number of other proteins evolve at a slower rate than those with fewer protein-protein interactions.
``Proteins with more interactors evolve more slowly, not because they are more important to the organism, but because a greater proportion of the protein is directly involved in its function,`` the authors wrote in Science.
This study comes
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
6-May-2002