1. Howard Hughes Medical Institute (R.P.P., S.G., A.H., J.N.I.), Department of Biochemistry (R.P.P., S.G., A.H., J.N.I.), St. Jude Children’s Research Hospital, Memphis, Tennessee 38105
2. Faculty of Health Sciences (Y.W.), Department of Microbiology and Immunology, Ben Gurion University of the Negev, Beer Sheva, Israel 84105