Mutant xylose-metabolizing enzyme and use thereof

The present invention provides information on a mutant xylose isomerase gene and a mutant protein with which it is possible to impart high xylose metabolic capacity to budding yeast. Also provided is a yeast strain having the mutant xylose isomerase gene. Additionally provided is an efficient method for producing a useful substance using the yeast strain. The present invention provides mutant Clostridium-phytofermentans-derived xylose isomerase (CpXI) having high xylose metabolic activity, the CpXI including an amino acid sequence corresponding to an amino acid sequence in which the number 63 threonine of SEQ ID NO: 11 of CpXI is substituted by isoleucine, lysine, glycine, or histidine and/or the number 162 valine is substituted by alanine. Also provided are: a transformed yeast having high ethanol productivity, the transformed yeast being obtained by transformation using a mutant CpXI gene that includes a codon mutation corresponding to a codon mutation in which the number 63 threonine of SEQ ID NO: 11 in a CpXI gene optimized for the preferred codon of budding yeast is substituted by isoleucine, lysine, glycine, or histidine and/or the number 162 valine is substituted by alanine; and a method for producing ethanol using the transformed yeast.