[1] Tufts Univ, Sch Med, Dept Mol Biol & Microbiol, 150 Harrison Ave, Boston, MA 02111 USA
[2] Tufts Univ, Dept Chem, 62 Talbot Ave, Medford, MA 02155 USA
[3] Tufts Univ, Sch Med, Howard Hughes Med Inst, 150 Harrison Ave, Boston, MA 02111 USA
[4] Washington Univ, Sch Med, Dept Mol Microbiol, St Louis, MO 63110 USA
[5] Tufts Univ, Sch Med, Genet Program, 150 Harrison Ave, Boston, MA 02111 USA
[6] Qiagen GmbH, D-40724 Hilden, Germany