[1] Icahn Sch Med Mt Sinai, 1425 Madison Ave, New York, NY 10029 USA
[2] Microsoft Res, Cambridge, MA 02142 USA
[3] European Bioinformat Inst, European Mol Biol Lab, Cambridge CB10 1SD, England
[4] Univ Calif Berkeley, Dept Plant & Microbial Biol, Berkeley, CA 94720 USA
[5] Univ Toronto, Donnelly Ctr Cellular & Biomol Res, Toronto, ON M5S 3E1, Canada