1. Institute of Life Sciences, Université Catholique de Louvain, Croix du Sud, 1, bte L7.04.01, B-1348 Louvain-la-Neuve, Belgium
2. Department of Molecular Microbiology, VIB, KU Leuven, B-3001 Leuven, Belgium
3. Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, K.U. Leuven, B-3001 Leuven, Belgium