EVOLVING A NEW FUNCTION: THE EBG CASE
Amber Eliza Trujillo, Ulfar Bergthorsson.
The University of New Mexico, Albuquerque, NM.
How do genes evolve novel functions? It has previously been shown that the ebg (evolved beta-galactosidase) locus in Escherichia coli can evolve a lactase activity in strains where the native lactase gene, lacZ, has been deleted. The natural substrate of the EBG protein is still unknown. We will test if gene amplification plays a role in the evolution of lactase activity of the ebg gene. The specific hypothesis that will be tested is whether selection for multiple copies of ebg on lactose medium facilitates the evolution of lactase activity of the gene. Duplications of the ebg gene will be constructed in lacZ deletion strains using lambda red technology. The rate of lactase evolution will be compared in strains that have 1 or 2 copies of ebg. If there is natural selection for increased gene copy-number of the wild-type ebg gene because of a preexisting insignificant lactase activity, strains with 2 copies of ebg are expected to evolve lactase activity at greater than 2 times the rate relative to the single copy strains. In preliminary experiments done using Berry Hall’s original lacZ deletion strains, early signs of adaptive mutability arose during the first generations of selection on minimal media. Small colonies of E. coli appeared to grow on glycerol-lactose plates, indicating that these colonies have promiscuous lactase activity. Sequencing and further tests will be performed on these lactose-using colonies to verify duplications of ebg, which, if present, will provide support for the amplification model.