1. Institute of Molecular and Cell Biology, University of Tartu, 23 Riia St; Tartu 51010 Estonia
2. Department of Biosciences; University of Helsinki, P.O. Box 56, Viikinkaari 9; FIN-00014 Helsinki Finland
3. Institute of Technology, University of Tartu, Nooruse 1; Tartu 50411 Estonia