The COG database: an updated version includes eukaryotes. - Roman L. Tatusov; Natalie D. Fedorova; John D. Jackson; Aviva R. Jacobs; Boris Kiryutin; Eugene V. Koonin; Dmitri M. Krylov; Raja Mazumder; Sergei L. Mekhedov; Anastasia N. Nikolskaya; B. Sridhar Rao; Sergei Smirnov; et al. (BMC Bioinform., 2003)