[1] Univ Helsinki, Dept Biosci, Div Genet, FIN-00014 Helsinki, Finland
[2] Univ Helsinki, Inst Biotechnol, FIN-00014 Helsinki, Finland
[3] Swedish Univ Agr Sci, Uppsala Biomed Ctr, Dept Plant Biol, S-75007 Uppsala, Sweden
[4] Norwegian Radium Hosp, Inst Canc Res, Dept Tumor Biol, N-0310 Oslo, Norway