Sesquiterpene lactones are a major class of plant secondary metabolites. These colourless, bitter, relatively stable, lipophilic molecules are the active constituents of a variety of medicinal plants used in traditional medicine. Here we try to identify genes from the pathway leading to costunolide biosynthesis. A germacrene A synthase and a sesquiterpene synthase oxidase were cloned from a cDNA library from feverfew and characterized by expression in yeast. Activity of the feverfew GAS was compared to that chicory GAS. We report on the products formed and the effect on buffer conditions on product yield
