The ethanol utilization pathway inAspergillus nidulansis a model system, which has been thoroughly elucidated at the biochemical, genetic and molecular levels. Three main ele-ments are involved: (a) high level expression of the positively autoregulated activator AlcR; (b) the strong promoters of the structural genes for alcohol dehydrogenase (alcA)and aldehyde dehydrogenase (aldA); and (c) powerful activa-tion of AlcRby the physiological inducer, acetaldehyde, produced from growth substrates such as ethanol and L-threonine. .
