[1] Univ Oregon, Inst Mol Biol, Eugene, OR 97403 USA
[2] Univ Oregon, Dept Phys, Eugene, OR 97403 USA
[3] Univ Oregon, Dept Chem, Eugene, OR 97403 USA
[4] Cent Labs Key Technol, Yokohama, Kanagawa 236, Japan
[5] Texas A&M Univ, Dept Biochem & Biophys, College Stn, TX 77483 USA