1. Institute of Physics, University of Tartu, W. Ostwald Str. 1, Tartu 50411, Estonia
2. School of Biochemistry, University of Bristol, Biomedical Sciences Building, University Walk, Bristol BS8 1TD, U.K.
3. Institute of Molecular and Cell Biology, University of Tartu, Riia 23, Tartu 51010, Estonia
4. Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia