Phylogenomic tree of domains (ToD) describing the evolution of 1,733 FSF domain structures. Taxa (FSFs) were colored according to their distribution () in the 981 genomes that were surveyed and used as characters to reconstruct the phylogenomic tree (data taken from [122, 123]). The most basal FSFs are labeled with SCOP alphanumeric identifiers (e.g., c.37.1 is the P-loop containing nucleoside triphosphate hydrolase FSF). Boxplots display the age (nd value) distribution of FSFs for the seven possible taxonomic groups. nd values were calculated directly from the tree [122] and define a timeline of FSF innovation, from the origin of proteins (nd = 0) to the present (nd = 1). The group of FSFs that are shared by the three domains of life (ABE) is the most ancient taxonomic group, which spans the entire time axis and their FSFs are widely distributed in genomes. The appearance of the BE group coincides with the first reductive loss of an FSF in Archaea. FSF structures specific to domains of life appear much later in evolution.
