[1] Univ Florence, Ctr Risonanze Magnet, I-50019 Sesto Fiorentino, Italy
[2] Max Planck Inst Biochem, D-82152 Martinsried, Germany
[3] Commiss European Communities, Res Directorate Gen, BE-1049 Brussels, Belgium
[4] Max Delbruck Ctr Mol Med, D-13122 Berlin, Germany
[5] Karolinska Inst, S-17177 Stockholm, Sweden
[6] Weizmann Inst Sci, Dept Neurobiol, IL-76100 Rehovot, Israel
[7] Weizmann Inst Sci, Dept Biol Struct, IL-76100 Rehovot, Israel