Partly human yeast show a common ancestor's lasting legacy

http://www.eurekalert.org/pub_releases/2015-05/uota-phy051415.php

Public Release: 21-May-2015
University of Texas at Austin

Despite a billion years of evolution separating humans from the baker's yeast in their refrigerators, hundreds of genes from an ancestor that the two species have in common live on nearly unchanged in them both, say biologists at The University of Texas at Austin. The team created thriving strains of genetically engineered yeast using human genes and found that certain groups of genes are surprisingly stable over evolutionary time.

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Although yeast consist of a single cell and humans have trillions of cells organized into complex systems, we share thousands of similar genes. Of those, about 450 are critical for yeast's survival, so researchers removed the yeast version of each one and replaced it with the human version and waited to see whether the yeast would die. Creating hundreds of new strains of yeast, each with a single human gene, resulted in many newly engineered strains -- nearly half, in fact -- that could survive and reproduce after having human genes swapped in for their ordinary ones.

"Cells use a common set of parts and those parts, even after a billion years of independent evolution, are swappable," said Edward Marcotte, professor in the university's Department of Molecular Biosciences and co-director of the Center for Systems and Synthetic Biology (CSSB). "It's a beautiful demonstration of the common heritage of all living things -- to be able to take DNA from a human and replace the matching DNA in a yeast cell and have it successfully support the life of the cell."

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This kind of gene swap experiment between humans and yeast has been done for single genes before, but this is the first large-scale study to swap hundreds of gene pairs. The large number of tests allowed team member Jon Laurent, a graduate student in the CSSB and co-author of the paper, to look for underlying rules for what makes a gene swappable.

Surprisingly, the best predictor of whether two genes could be successfully swapped was not how similar their genetic sequences were, but rather which modules they were part of. A module is a group of genes that work together to do something useful, such as produce cholesterol to build cell walls. All the genes from the same module tended either to be swappable between humans and yeast, or not.

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