1. Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, U.S.A.
2. Fukuda Initiative Research Unit, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
3. Institute of Biotechnology, Program in Cellular Biotechnology, FIN-00014, University of Helsinki, Helsinki, Finland
4. Harvard Microchemistry and Proteomics Analysis Facility, Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, U.S.A.