1. Department of Biochemical Sciences “A. Rossi Fanelli”, CNR Institute of Molecular Biology and Pathology and Istituto Pasteur-Fondazione Cenci Bolognetti, University of Rome “La Sapienza”, Piazzale Aldo Moro 5, 00185 Rome, Italy, CNR Institute of Cell Biology, 32 Via Ramarini, 00016 Monterotondo, Rome, Italy, and Bernhard-Nocht-Institut für Tropenmedizin, 74 Bernhard-Nocht-Strasse, 20359 Hamburg, Germany