Overall numbers of domain fusions estimated using the COGs and interkingdom domain fusions encoded in completely sequenced genomes. The data for estimating the overall number of domain fusions were from the current COG release , which does not include several bacterial and archaeal species (for example, Aeropyrum pernix and Deinococcus radiodurans) that have been analyzed in the present work (Table 1). Accordingly, the data for these genomes are not shown in the figure. Species name abbreviations: Af, Archaeoglobus fulgidus; Mj, Methanococcus jannaschii; Mth, Methanobacterium thermoautotrophicum; Ph, Pyrococcus horikoshii; Sc, Saccharomyces cerevisiae; Aa, Aquifex aeolicus; Tm, Thermotoga maritima; Ssp, Synechocystis sp.; Ec, Escherichia coli; Bs, Bacillus subtilis; Mtu, Mycobacterium tuberculosis; Hi, Haemophilus influenzae; Hp, Helicobacter pylori; Mg; Mycoplasma genitalium; Mp, Mycoplasma pneumoniae; Bb, Borrelia burgdorferi; Tp, Treponema pallidum; Ct, Chlamydia trachomatis; Cp, Chlamydophila pneumoniae; Rp, Rickettsia prowazekii.