SECRETION AND OVERPRODUCTION OF CARBOXYPEPTIDASE-Y BY A SACCHAROMYCES-CEREVISIAE-SSL1 MUTANT STRAIN

Carboxypeptidase Y (CPY; EC 3.4.16.1) is the yeast vacuolar protease. To have CPY secreted and to increase its secretion level, we tried to express the prepro-CPY gene under the control of the inducible GAL10 p romoter or constitutive ENO1 promoter on a multicopy plasmid. In the s trains KK4, PEP4, and A2-1-1A, carrying the CPY expression plasmid, ac tive CPY was not detected in the culture broth although the CPY activi ty was greatly increased inside the cells. In contrast, when we used a strain that contained the ssl1 (super-secretion of lysozyme) mutation , a large amount of active CPY (about 10-50 mg/liter) was detected in the culture broth. The ssl1 mutants secreted active CPY when the CPY l evel was increased by expressing it under the control of a strong prom oter on a multicopy plasmid, while the endogenous expression of chromo somal CPY gene in the same ssl1 mutant caused a deficiency in the proc essing of pro-CPY to mature CPY.