α‐Factor directed expression of the human epidermal growth factor in Saccharomyces cerevisiae

Abstract

Expression kinetics of the human Epidermal Growth Factor (hEGF) from the alpha-factor prepro region in a 2-mum based plasmid was studied in Saccharomyces cerevisiae. Production of hEGF was highly medium de pendent as a chemically defined, nonenriched media had a significantly lower yield than did enriched media. Also cells grown on yeast nitrogen base without amino acids with casamino acids degraded the hEGF after cell growth as opposed to a yeast extract, peptone, and dextrose (YEPD) medium, which elicited no measurable extracellular proteolysis of the hEGF. alpha-factor directed production kinetics of hEGF on the YEPD medium were growth associated, secretion limitations and extracellular degradation were negligible, and the hEGF was nearly 100% selectively secreted. With sufficient agitation, shake flask experiments were representative of aerated controlled batch fermentations. No effect of high cell density was observed on cell growth or hEGF production kinetics. The hollow fiber bioreactor had no direct effect on the substrate or protein yields of S. cerevisiae, however the low oxygen transfer capacity of the membrane was not sufficient to support respiration.