1. Yale University School of Medicine, New Haven, CT 06511, USA.
2. Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
3. Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
4. Columbia University School of Medicine, New York, NY 10032, USA.
5. Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
6. Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455, USA.