1. Stowers Institute for Medical Research, Kansas City, MO 64110, USA
2. Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA
3. Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA
4. European Bioinformatics Institute (EMBL-EBI), European Molecular Biology Laboratory, Wellcome Genome Campus, Hinxton, Cambridge CB10 1SD, UK