1. Division of Genetics and Physiology, Department of Biology, FI-20014 University of Turku, Turku, Finland
2. Institute of Biotechnology, Viikki Biocenter, P. O. Box 56, FI-00014 University of Helsinki, Helsinki, Finland
3. Division of Biochemistry and Biotechnology, Department of Biosciences, FI-00014 University of Helsinki, Helsinki, Finland
4. Department of Biochemistry, FI-20014 University of Turku, Turku, Finland
5. Department of Experimental Medical Science, Lund University, SE-221 84, Lund, Sweden
6. Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA