[1] UNIV CALIF LOS ANGELES, DEPT MICROBIOL & MOLEC GENET, LOS ANGELES, CA 90024 USA
[2] TUFTS UNIV, SCH MED, DEPT PATHOL, BOSTON, MA 02111 USA
[3] TUFTS UNIV, SCH MED, DEPT MOLEC BIOL & MICROBIOL, BOSTON, MA 02111 USA
[4] UNIV CALIF LOS ANGELES, HOWARD HUGHES MED INST, LOS ANGELES, CA 90024 USA
[5] UNIV CALIF LOS ANGELES, INST MOLEC BIOL, LOS ANGELES, CA 90024 USA