[1] Scripps Res Inst, Dept Mol Biol, La Jolla, CA 92037 USA
[2] Scripps Res Inst, Dept Cell Biol, La Jolla, CA 92037 USA
[3] Univ Utah, Sch Med, Dept Pathol, Salt Lake City, UT 84112 USA
[4] Univ Alabama Birmingham, Dept Microbiol, Birmingham, AL 35294 USA