[1] Univ Calif Los Angeles, Howard Hughes Med Inst, Los Angeles, CA 90095 USA
[2] Univ Calif Los Angeles, Dept Mol Cell & Dev Biol, Los Angeles, CA 90095 USA
[3] Univ Calif Los Angeles, Sch Med, Dept Immunol & Med Microbiol, Los Angeles, CA 90024 USA
[4] Univ Calif Riverside, Dept Biol, Riverside, CA 92521 USA
[5] Univ Kentucky, Med Ctr, Dept Biochem, Lexington, KY 40536 USA