A polynucleotide encoding the amino acid shown in SEQ ID NO:2 or SEQ ID NO: 5, or encoding an amino acid sequence having not less than 98% identity thereto preferably a polynucleotide comprising replacement of the amino acid corresponding to glutamic acid at position 1202 of SEQ ID NO:2 (position 177 of SEQ ID NO:5) with glycine, replacement of the amino acid corresponding to glutamic acid at position 1056 (position 31 of SEQ ID NO:5) with valine, and replacement of the amino acid corresponding to alanine at position 2199 (position 1174 of SEQ ID NO:5) with threonine.
