[1] Max Planck Gesell, Fritz Haber Inst, D-14195 Berlin, Germany
[2] Free Univ Berlin, Inst Chem, Forschungszentrum Elektronenmikroskopie, D-14195 Berlin, Germany
[3] Humboldt Univ, Inst Biol Biophys, Math Nat Fak 1, D-10115 Berlin, Germany
[4] Univ London Imperial Coll Sci Technol & Med, Wolfson Labs, Dept Biochem, London SW7 2AY, England
[5] Inst Mol Biol & Tumorforsch, D-35037 Marburg, Germany