Expression of invertase activity in Yarrowia lipolytica and its use as a selective marker

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Abstract
Few selective markers are available for the transformation of the industrial yeast Yarrowia lipolytica, and those that are require the use of specialized hosts (e.g., auxotrophs, antibiotic sensitive). To enable the transformation of any Y. lipolytica strain, we used the property that Y. lipolytica cannot use sucrose as a sole carbon source. We have constructed a gene fusion where the Saccharomyces cerevisiae SUC2 gene is placed under the control of the promoter and signal sequence of the Y. lipolytica XPR2 gene, which encodes an Alkaline Extracellular Protease (AEP). Strains bearing this fusion express invertase activity and grow on sucrose as a carbon source. The activity follows the same regulation as does the alkaline extracellular protease, is secreted into the periplasm and confers a Suc+ phenotype. It was shown that this chimeric gene could be used as a dominant marker for transformation in a one-step procedure.