[1] Univ Calif San Diego, Sect Cell & Dev Biol, La Jolla, CA 92093 USA
[2] Univ Calif San Diego, Dept Pharmacol, La Jolla, CA 92093 USA
[3] Univ Calif San Diego, Dept Chem & Biochem, La Jolla, CA 92093 USA
[4] Univ Calif San Diego, Howard Hughes Med Inst, La Jolla, CA 92093 USA
[5] Salk Inst Biol Studies, Plant Biol Lab, La Jolla, CA 92037 USA
[6] Salk Inst Biol Studies, Howard Hughes Med Inst, La Jolla, CA 92037 USA