1. Department of Biology (M.A.T.), Curriculum in Genetics (J.L.D.), Department of Microbiology and Immunology (J.L.D.), and Carolina Center for Genome Sciences (J.L.D.), University of North Carolina, Chapel Hill, North Carolina 27599–3280; and Sainsbury Laboratory, John Innes Center, Colney, Norwich NR4 7UH, United Kingdom (J.D.G.J.)