[1] Stanford Univ, Genome Technol Ctr, Palo Alto, CA 94306 USA
[2] Yale Univ, Sch Med, Dept Genet, New Haven, CT 06520 USA
[3] Stanford Univ, Dept Biol Sci, Stanford, CA 94305 USA
[4] Stanford Univ, Dept Dev Biol, Stanford, CA 94305 USA
[5] Stanford Univ, Dept Genet, Stanford, CA 94305 USA
[6] Stanford Univ, Dept Biochem, Stanford, CA 94305 USA
[7] Stanford Univ, Howard Hughes Med Inst, Stanford, CA 94305 USA
[8] European Mol Biol Lab, Dev Biol Program, D-69117 Heidelberg, Germany
[9] Univ Oregon, Inst Mol Biol, Eugene, OR 97403 USA