This thesis is divided into four chapters describing experiments performed to further our understanding of the characteristics of the alcohol dehydrogenase (ADH) genes encoding ADH isozymes, responsible for the final step in the alcoholic fermentation of xylose-fermenting yeast Pichia stipitis.; Isolation and functional analyses of two ADH genes (PsADH1 and PsADH2) indicate that the deduced PsADH gene products are highly conserved and show considerable identity with other yeast ADHs, that PsADH1 isozyme plays a major role in xylose fermentation, and that the two PsADH isozymes are equivalent in their ability to oxidize ethanol to allow cell growth.; Analysis of PsADH1 and PsADH2 regulation suggest that transcription of PsADH1 is negatively controlled by oxygen. This hypoxic regulation may be mediated by heme. The expression of PsADH2 appears to be feedback regulated. Overall, the regulation of the ADH system in P. stipitis and other yeasts exhibits substantial differences despite the high sequence conservation of the ADH genes. We present a model for the mechanism by which fermentation and respiration are regulated in P. stipitis and describe future experiments.
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