ABSTRACT
Haploid cells of Saccharomyces cerevisiae belong to one or the other of mating types a and α. The response to a and α pheromones is controlled by the mating type locus. Transformants secreting the α-factor were detected by a halo method using a lawn of cells supersensitive to α. The idea was that matα2 cells containing an α-factor structural gene on a high copy number plasmid would produce more α-factor than could be degraded. The chimeric gene directed the synthesis of invertase that was efficiently secreted into the periplasmic space, allowing growth on sucrose-containing media. Interestingly, the extracellular invertase produced from the fusion gene was somewhat underglycosylated. The invertase produced by SUC2 alone had molecular weights in the range 100 to 125 kDa, whereas invertase produced by cells carrying the chimeric gene was in the range 75 to 91 kDa. The PHO5 gene of S. cerevisiae encodes an acid phosphatase whose synthesis is repressed at high phosphate concentration.
