1. Department of Molecular Enzymology Kumamoto University Graduate School of Medical Sciences Honjo Kumamoto 860‐8556 Japan
2. Division of Evolutionary Genetics Department of Population Genetics National Institute of Genetics Mishima Shizuoka 411‐8540 Japan
3. Department of Microbiology Kinki University Faculty of Medicine Osaka‐Sayama Osaka 589‐8511 Japan