Positive and negative selection LYS5MX gene replacement cassettes for use in Saccharomyces cerevisiae.

Novel MX cassettes are described that contain the open reading frames (ORFs) of Saccharomyces cerevisiae or Candida albicans LYS5. The LYS5MX and CaLYS5MX cassettes, the targeting efficiencies of which are equivalent to those of other MX cassettes, are positively selected for Lys+ in a lys5 background. Unlike most of the other MX cassettes, the LYS5MX cassettes are also negatively selectable (alpha-aminoadipate-resistant), which will allow the use of the LYS5MX cassettes in plasmid shuffling and will also greatly facilitate marker recycling.