[Yeast (Saccharomyces cerevisiae) secretory expression vector maintained stably in Pro3+ transformants in rich...

A yeast (Saccharomyces cerevisiae) secretory expression vector containing PRO3 gene was constructed (pCBy310). beta HCG(Human choriogonadotropin beta subunit)-cDNA was inserted into pCBy310 to form a recombinant plasmid pCBy314. Since yeast proline auxotroph will not survive in rich medium (YPD), YPD could be used as a selection pressure, and pCBy314 could be maintained mitotically stable in transformants of yeast Pro3- auxotroph (MB299-7A) in rich medium. At an improved, yet not optimized cultural condition, the expression of beta HCG in culture medium was 650 micrograms/L. Our results showed not only that YPD could be used as a selection medium, but also that yeast grew better in YPD so as to increase the gene expression product, and that the component of YPD was simple and cheap. Our data suggested that PRO genes might be used widely in constructing vectors to clone and express foreign genes in yeast so that rich medium can be used as a selection pressure for direct selection.