1. Watson School of Biological Sciences, Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
2. Department of Genetics, Center for Genetics and Genomics, Brigham and Women's Hospital, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115, USA.
3. Expression Analysis, Inc., 4324 South Alston Avenue, Durham, NC 27713, USA.