A second set of loxP marker cassettes for Cre-mediated multiple gene knockouts in budding yeast.

Heterologous markers are important tools required for the molecular dissection of gene function in many organisms, including Saccharomyces cerevisiae. Moreover, the presence of gene families and isoenzymes often makes it necessary to delete more than one gene. We recently introduced a new and efficient gene disruption cassette for repeated use in budding yeast, which combines the heterologous dominant kan(r) resistance marker with a Cre/loxP-mediated marker removal procedure. Here we describe an additional set of four completely heterologous loxP-flanked marker cassettes carrying the genes URA3 and LEU2 from Kluyveromyces lactis, his5(+) from Schizosaccharomyces pombe and the dominant resistance marker ble(r) from the bacterial transposon Tn5, which confers resistance to the antibiotic phleomycin. All five loxP--marker gene--loxP gene disruption cassettes can be generated using the same pair of oligonucleotides and all can be used for gene disruption with high efficiency. For marker rescue we have created three additional Cre expression vectors carrying HIS3, TRP1 or ble(r) as the yeast selection marker. The set of disruption cassettes and Cre expression plasmids described here represents a significant further development of the marker rescue system, which is ideally suited to functional analysis of the yeast genome.