SEQUENCE AND ANALYSIS OF AN ALDOSE (XYLOSE) REDUCTASE GENE FROM THE XYLOSE-FERMENTING YEAST PACHYSOLEN-TANNOPHILUS

A xylose reductase gene was isolated from the xylose-fermenting yeast Pachysolen tannophilus as a cDNA clone by selecting clones that hybrid ized specifically to xylose-inducible messenger RNA. Use of the cDNA c lone as a probe in Northern hybridizations identified a xylose-inducib le mRNA species large enough to encode a 36 kDa xylose reductase prote in known to be produced by this yeast. A corresponding genomic clone w as isolated as a 3 kb EcoRI fragment that specifically hybridized to t he cDNA clone. The sequence of the cDNA and the largest open reading f rame of the genomic clone are identical. The predicted translation pro duct exhibits: (1) significant sequence identity with a previously pub lished N-terminal amino acid sequence from purified P. tannophilus xyl ose (aldose) reductase protein exhibiting NADH/NADPH-dependent activit ies (aldose reductase, EC 1.1.1.21); (2) identity with a protein compo sed of 317 amino acid residues with a calculated molecular mass of 36. 2 kDa, equivalent to that reported for purified P. tannophilus xylose reductase; and (3) considerable sequence similarity to, and features o f, a superfamily of oxidoreductases. This sequence is deposited as Gen Bank Accession Number U40706.