1. Institute of Organic Chemistry and Biochemistry ASCR, Prague 166 10, Czech Republic
2. Department of Biochemistry and Microbiology, University of Chemistry and Technology, Prague 166 28, Czech Republic
3. Cancer Center and Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, United States
4. Department of Cell Biology, Charles University in Prague, Faculty of Science, Prague 128 44, Czech Republic