[1] Dartmouth Coll Sch Med, Dept Biochem, Hanover, NH 03755 USA
[2] Univ Tokyo, RCAST, Dept Mol Biol & Med, Tokyo 1538904, Japan
[3] Salk Inst Biol Studies, Howard Hughes Med Inst, Gene Express Lab, La Jolla, CA 92037 USA
[4] Harvard Univ, Sch Med, Howard Hughes Med Inst, Dept Pathol, Boston, MA 02115 USA