초록
<P>The industrial yeast <I>Candida utilis</I> can grow on media containing xylose as sole carbon source, but cannot ferment it to ethanol. The deficiency might be due to the low activity of NADPH-preferring xylose reductase (XR) and NAD<SUP>+</SUP>-dependent xylitol dehydogenase (XDH), which convert xylose to xylulose, because <I>C. utilis</I> can ferment xylulose. We introduced multiple site-directed mutations in the coenzyme binding sites of XR and XDH derived from the xylose-fermenting yeast <I>Candida shehatae</I> to alter their coenzyme specificities. Several combinations of recombinant and native XRs and XDHs were tested. Highest productivity was observed in a strain expressing CsheXR K275R/N277D (NADH-preferring) and native CsheXDH (NAD<SUP>+</SUP>-dependent), which produced 17.4 g/L of ethanol from 50 g/L of xylose in 20 h. Analysis of the genes responsible for ethanol production from the xylose capacity of <I>C. utilis</I> indicated that the introduction of CsheXDH was essential, while overexpression of CsheXR K275R/N277D improved efficiency of ethanol production.</P>