[1] Univ Calif Berkeley, Dept Mol & Cell Biol, Berkeley, CA 94720 USA
[2] Univ Calif Berkeley, Virus Lab, Berkeley, CA 94720 USA
[3] Univ Calif Berkeley, Howard Hughes Med Inst, Berkeley, CA 94720 USA
[4] Univ Calif Berkeley, Dept Mol & Cell Biol, Berkeley, CA 94720 USA