1. Institute of Medical Technology, University of Tampere, FIN-33014 Tampere
2. Program of Developmental and Reproduction Biology, Biomedicum Helsinki, and Department of Virology, Haartman Institute, University of Helsinki, FIN-00014 Helsinki
3. The Walter and Eliza Hall Institute of Medical Research and the Cooperative Research Center for Cellular Growth Factors, Parkville, Victoria 3050, Australia
4. Department of Clinical Microbiology, Tampere University Hospital, FIN-33521 Tampere, Finland