1. Department of Computational Biology, Graduate School of Frontier Sciences, University of Tokyo, Kshiwanoha 5-1-5, Kashiwa, Chiba 277-8568, Japan.
2. Department of Biophysics and Biochemistry, Graduate School of Science, CREST, Japan Science and Technology Agency, University of Tokyo, Hongo 7-3-1, Bunkyo-ku,Tokyo 113-0033, Japan.