1. Department of Molecular Biotechnology, Graduate School of Advanced Sciences of Matter, Hiroshima University, 1‐3‐1 Kagamiyama, Higashi‐Hiroshima 739‐8530, Japan; telephone: 81‐082‐424‐7752; fax: 81‐082‐424‐7752
2. Research Center, TOYOBO Co., Ltd., Otsu, Japan