Figure 2.

Ancient universal cores and derived peripheries support a biphasic process of accretion. (A) Venn diagrams describe censuses of protein structural domains defined at fold superfamily (FSF) level of structural classification of the SCOP taxonomy, Gene Ontology (GO) terms of molecular functions, RNA families defined by the Rfam database, and homologies of ribosomal proteins (r-proteins). The universal repertoires shared by Archaea, Bacteria, and Eukarya are colored in red. (B) Model of accretion explaining the Venn diagrams. In phase 1, biological repertoires of parts accrete into universal cores, which in phase 2 diversify together with the evolving organisms of the 3 cellular superkingdoms of life.