Figure 4

Apparent complex origins of some key functional systems of eukaryotes. The likely origins of proteins and domains are shown by color code for three key functional systems of the eukaryotic cell: (a) B-family DNA polymerases comprising the core of the replication apparatus (triangles show Zn-finger modules; crosses indicate inactivated enzymatic domains; pol, polymerase; exo, exonuclease) [100]; (b) RNA interference (RNAi) machinery (RdRp, RNA-dependent RNA polymerase) [70]; and (c) cell division apparatus (the Vps4 ATPase and Snf7-like proteins comprise the ESCRT-III machinery) and cytoskeleton [97, 98, 105, 113]. The domains are not drawn to scale. The light blue color of the three amino-terminal domains of Polε indicates the substantial sequence divergence from the homologous domains of other eukaryotic polymerases.