1. Center for Biological Sequence Analysis (S.R., H.B.N.) and Department of Systems Biology (S.R., P.F., H.B.N.), Technical University of Denmark, Lyngby, Denmark DK–2800
2. Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway N–7491 (P.B., A.M.B.)
3. Department of Biology, University of Copenhagen, Copenhagen, Denmark, DK–2200 (M.C.S.-R., S.B., J.M.); and
4. Department of Biology and Biotechnology, University of Rome La Sapienza, 00185 Rome, Italy (P.C.)