Table 1

Apparent origins of some key functional systems and molecular machines of eukaryotes

System/complex/function

Inferred origins

References

DNA replication and repair machinery

Archaeal, with either crenarchaeotal or euryarchaeotal affinities for DNA polymerases and other central replication proteins; a mix of archaeal and bacterial for repair enzymes

[99,100,128]

Transcription machinery

Archaeal; at least two RNA polymerase subunits of crenarchaeotal/korarchaeotal origin

[63,86,89,93,94,129]

Translation apparatus, including ribosomes

Mostly archaeal; some aminoacyl-tRNA synthetases displaced with bacterial homologs

[91,130]

Cell division and membrane remodeling systems; phagocytosis

Primarily archaeal (Crenarchaeota) but some key regulators like Ras superfamily GTPases of bacterial origin

[105,113,114]

Cytoskeleton

Primarily archaeal; euryarchaeal affinity for tubulin, crenarchaeotal for actin

[96,105]

Proteasome: regulated proteolysis

Archaeal

[110]

Ubiquitin signaling: regulated proteolysis and protein topogenesis

Archaeal but origin of some essential components, such as E2 and E3 ubiquitin ligases, uncertain

[115,131]

Exosome: regulated RNA degradation

Archaeal

[132]

Nuclear pore complex: nucleocytosolic transport

Bacterial; some key proteins of the nuclear pore complex repetitive and of uncertain origin

[28]

Chromatin/nucleosomes

Complex mix of archaeal and bacterial

[66]

RNA interference

Hybrid of archaeal and bacterial

[70,133,134]

Endomembrane system/endoplasmic reticulum

Complex mix of archaeal and bacterial

[9,10,105]

Mitochondrion/electron transfer chain

Bacterial

[81,135]

Koonin Genome Biology 2010 11:209   doi:10.1186/gb-2010-11-5-209