The chronological development of the fermentation industry may be represented as five overlapping stages microbial cells such that the recipients are capable of synthesizing 'foreign' (or heterologous) proteins. A wide range of microbial cells have been used as hosts for such systems including Escherichia coli, Saccharomyces cerevisiae and filamentous fungi. Products produced by such genetically engineered organisms include interferon, insulin, human serum albumin, factors VIII and IX, epidermal growth factor, calf chymosin and bovine somatostatin. Important factors in the design of these processes include the secretion of the product, minimization of the degradation of the product and control of the onset of synthesis during the fermentation, as well as maximizing the expression of the foreign gene. These aspects are considered in more detail in Chapters 3 and 4.
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