[1] Univ Michigan, Cellular & Mol Biol Program, Ann Arbor, MI 48109 USA
[2] Univ Michigan, Dept Mol Cellular & Dev Biol, Ann Arbor, MI 48109 USA
[3] Univ Michigan, Howard Hughes Med Inst, Ann Arbor, MI 48109 USA
[4] Univ Alabama Birmingham, Dept Microbiol, Birmingham, AL 35294 USA