Host cell properties and external pH affect proinsulin production by Saccharomyces yeast

The expression of a hybrid gene encoding an α-factor prepro leader peptide-miniproinsulin (MPI) fusion [MPI is the same as the LysArg human insulin precursor described by Thim et al. (1986)] was tested in a series of isogenic yeast strains to investigate the influence of some genetic and physiological factors on heterologous production in yeast. We found that: (i) an MFα1 gene disruption in haploid cells, as well as MFα1 gene product expression in diploid cells, do not affect the MPI secretion level; (ii) under conditions of exogenous leucine availability, MPI production is hindered by leucine auxotrophy (a leu2 mutation); (iii) rho− mutations increase the per-cell MPI yield approximately three-fold; (iv) the MPI yield is apparently dependent on the pH of the culture medium: the higher the external pH, the larger the per-cell MPI yield.