FIGURE 9.

Model scheme for the evolution of bacterial tubulin. The α- and β-tubulin proto-proteins appeared in a primitive eukaryotic cell by gene duplication from a tubulin ancestor, which had a GTP-binding domain (blue) and a GTPase-activating domain (red). Shortly after duplication, both genes were transferred to a bacterium, one possibility being a Verrucomicrobal ancestor of Prosthecobacter. Primitive tubulins coassembled into filamentous heteropolymers that underwent divergent more extensive evolution in eukarya than in bacteria.