[1] Univ Edinburgh, Inst Cell & Mol Biol, Wellcome Trust Ctr Cell Biol, Edinburgh EH9 3JR, Midlothian, Scotland
[2] Univ Paris Sud, Inst Curie, UMR 2027, F-91405 Orsay, France
[3] Washington Univ, Sch Med, Dept Biochem & Mol Biophys, St Louis, MO 63110 USA
[4] Univ Zurich, Dept Vet Biochem, CH-8057 Zurich, Switzerland