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bioreactor studies of heterologous protein production by ...

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foreign plasmids. One major chalienge in aimmezcial <strong>production</strong> <strong>of</strong> recombinant products<br />

is to maintain the engineered genetic stabüity <strong>of</strong> the recombinant =Ils A concerted effort<br />

involving geneticists, microbiologists. and biochemical engineers is required to overcome<br />

the genetic instabiity problem.<br />

1.1. Importance <strong>of</strong> Recombinant Saccharomyces cemisiae<br />

Earlier research on recombinant DNA technology focused mainly on using procaryotes<br />

such as Eschenchia coli as host for expression <strong>of</strong> recombinant products. It soon became<br />

obvious that procaryotes were far h m the ideal hosts. Attempts to hnd a more suitable<br />

host led Unmediately to the weli known yeast, Saccharomyces cerevisiae. brewer's or<br />

baker's yeast Unlike E. coli, S. cerevisiae hcks detectabïe endotoxins and is generally<br />

regarded as a safe (GRAS) organism for the <strong>production</strong> <strong>of</strong> food and pharmaœutical<br />

products. Moreover, the rapid advancements in understanding yeast biology and genetics<br />

have made yeast genetic manipulation datively easy. In addition, yeast grows much<br />

faster than other potential eucaryotic hosts such as animai cells; it &O is able to<br />

glycosylate <strong>protein</strong>s and to cany out postmslational foldings and modifications <strong>of</strong><br />

eucaryotic gene products to ensure their stnicniral integrity and biologicai activity.<br />

Furthemo~. yeast bioprocesses had been weU established and may be easiiy adapted to<br />

the <strong>production</strong> <strong>of</strong> recombinant <strong>protein</strong>s. Finally, expression in yeast may aüow naturai<br />

extraceiiuiar release <strong>of</strong> the <strong>protein</strong> because <strong>of</strong> a secretion systern that is similar to that <strong>of</strong><br />

higher eucaryotes. BiologicaIIy active, secreted products are substantiaiiy easier to recover

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