Isoamyl alcohol (i-AmOH)
and isoamyl acetate (IsOAc) are important flavor components of yeast-fermented alcoholic beverages. i-AmOH is formed via the leucine
synthetic pathway or via the Ehrlich mechanism from leucine by the
branched-chain amino acid aminotransferase encoded by BAT1 and
BAT2 genes. IsOAc is synthesized from i-AmOH and acetyl CoA by
alcohol acetyltransferase encoded by the ATF1 gene. We show that
the BAT2 gene product plays an important role for i-AmOH and
IsOAc production by analyzing bat2 null mutants and transformants
with multi-copy plasmids containing the BAT2 gene. As well, the
effects of the nitrogen source on i-AmOH and IsOAc production are
investigated by a fermentation test using synthetic medium which
contains various concentrations of the nitrogen source. Results showed
that the production of i-AmOH and IsOAc increased with increasing
concentrations of the nitrogen source until the system was saturated.
Further addition of the nitrogen source reduced the yields of i-AmOH and
IsOAc. RNA blot analysis showed that transcription of BAT2 and
LEU2 increased with increasing i-AmOH production and ATF1
transcription increased with increasing concentrations of the nitrogen
source. These data suggest that transcription of BAT2 and
LEU2 is co-regulated by the nitrogen source and ATF1
transcription is activated by the nitrogen source.
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