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 hybridized specifically to xylose-inducible messenger RNA. Use of the cDNA clone as a probe in Northern hybridizations identified a xylose-inducible mRNA species large enough to encode a 36 kDa xylose reductase protein known to be produced by this yeast. A corresponding genomic clone was isolated as a 3 kb EcoRI fragment that specifically hybridized to the cDNA clone. The sequence of the cDNA and the largest open reading frame of the genomic clone are identical. The predicted translation product exhibits: (1) significant sequence identity with a previously published N-terminal amino acid sequence from purified P. tannophilus xylose (aldose) reductase protein exhibiting NADH/NADPH-dependent activities (aldose reductase, EC 1.1.1.21); (2) identity with a protein composed 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 of, a superfamily of oxidoreductases. This sequence is deposited as GenBank Accession Number U40706.