1. Helsinki Institute of Life Science, University of Helsinki 1 , Helsinki, Finland
2. Institute of Biotechnology, University of Helsinki 2 , Helsinki, Finland
3. Faculty of Biological and Environmental Sciences, University of Helsinki 3 , Helsinki, Finland
4. Karolinska Institutet 4 Department of Cell and Molecular Biology, , Stockholm, Sweden
5. MRC Laboratory of Molecular Biology 5 , Cambridge, UK