1. Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada, H3A 2B2
2. Laboratoire d'Immunoretrovirologie, Centre de Recherche d'Infectiologie – CHUL, Quebec, Canada, G1V 4G2
3. Department of Biochemistry, McGill University, Montreal, Quebec, Canada, H3G 1Y6
4. Cell Biology and Biophysics Unit, EMBL, 69117 Heidelberg, Germany