Growth phase modulation of the productivity of α-galactosidase in budding yeast cultures

In Saccharomyces cerevisiae, protein secretion into the growth medium depends on environmental factors

In the budding yeast Saccharomyces cerevisiae the cell wall, mainly composed of mannoproteins and glucans, constitutes a barrier to protein excretion in the growth medium. In this paper we have studied the effects of different environmental parameters on excretion of Escherichia coli beta-galactosidase obtained by exploiting the glucoamylase II signal sequence. Excretion of the unglycosylated beta-galactosidase was detectable only in cells grown in rich medium, was affected by temperature (36 degrees C > 30 degrees C >> 24 degrees C) and slightly stimulated by reducing agents. On the contrary, glycosylated proteins, such as alpha-galactosidase and glucoamylase II, were excreted to a good extent under all tested conditions of medium composition, growth temperature and pH. These data indicate that optimization of environmental parameters may help the excretion of heterologous proteins, offering advantages for protein purification.

Heterologous gene expression in continuous cultures of budding yeast

In a previous paper we have studied the expression of beta-galactosidase from Escherichia coli, driven from the inducible GAL1-10/CYC1 hybrid promoter, in batch cultures of budding Saccharomyces cerevisiae and have described operating conditions for maximal productivity. In this paper we show that the plasmid instability in continuous cultures can be overcome by utilizing appropriate selection markers and a high copy number vector. The maximal level of expression is influenced by the dilution rate. Moreover, enzyme accumulation appears to depend also upon the degree of oxygenation. A possible explanation of these modulations is discussed, taking into account the interactions of the UAS-GAL and TATA-CYC1 elements.