Each rectangle signifies an enzyme of the pyrimidine biosynthesis pathway, indicated by its gene name and COG number. Alternative enzymes catalyzing the same reaction are shown side-by-side. Each COG is accompanied by the list of organisms represented in it (the phyletic pattern, see 2.2.6). The species abbreviations and order are as follows: a, Archaeoglobus fulgidus; o, Halobacterium sp.; m, methanogens (M. jannaschii and M. thermoauto-trophicum); p, thermoplasmas (T. acidophilum and T. volcanii); k, pyrococci (P. horikoshii and P. abyssi); z, Aeropyrum pernix; y, yeast (Saccharomyces cerevisiae); q, Aquifex aeolicus; v, Thermotoga maritima; d, Deinococcus radiodurans; r, mycobacteria (M. tuberculosis and M. leprae); l, streptococci (Lactococcus lactis and Streptococcus pyogenes); b, bacilli (B. subtilis and B. halodurans); c, Synechocystis sp.; e, Escherichia coli; f, Pseudomonas aeruginosa; g, Vibrio cholerae; h, Haemophilus influenzae; s, Xylella fastidiosa; n, Neisseria meningitidis; u, Helicobacter pylori and Campylobacter jejuni; j, Mesorhizobium loti and Caulobacter crescentus; x, Rickettsia prowazekii; i, chlamydiae (C. trachomatis and C. pneumoniae); t, spirochetes (Borrelia burgdorferi and Treponema pallidum); and w, mycoplasmas (M. genitalium, M. pneumoniae, and Ureaplasma urealyticum).