HOST-CELL PROPERTIES AND EXTERNAL PH AFFECT PROINSULIN PRODUCTION BY SACCHAROMYCES YEAST

The expression of a hybrid gene encoding an alpha-factor prepro leader peptide-miniproinsulin (MPI) fusion [MPI is the same as the LysArg hu man 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 MF alpha l gene disruption in haploid cells, a s well as MF alpha l gene product expression in diploid cells, do not affect the MPI secretion level; (ii) under conditions of exogenous leu cine availability, MPI production is hindered by leucine auxotrophy (a leu2 mutation); (iii) rho(-) mutations increase the per-cell MPI yiel d approximately three-fold; (iv) the MPI yield is apparently dependent on the pH of the culture medium: the higher the external pH, the larg er the per-cell MPI yield.