1. Institute for Bioscience and Biotechnology Research and Department of Cell Biology and Molecular Genetics, University of Maryland, 9600 Gudelsky Drive; Rockville Maryland 20850
2. Genome Center, University of California, Davis, 451 Health Sciences Drive; Davis California 95616
3. University of Basel, Biozentrum & SIB Swiss Institute of Bioinformatics; Basel Switzerland
4. Department of Physics and Istituto Pasteur - Fondazione Cenci Bolognetti; Sapienza University of Rome, P.le Aldo Moro, 5; Rome 00185 Italy