[1] Univ Calif Santa Cruz, Dept Biol, Sinsheimer Labs, Santa Cruz, CA 96054 USA
[2] Univ Calif San Francisco, Howard Hughes Med Inst, Dept Anat, San Francisco, CA 94143 USA
[3] Univ Calif San Francisco, Howard Hughes Med Inst, Dept Biochem & Biophys, San Francisco, CA 94143 USA