Table 1 Apparent origins of some key functional systems and molecular machines of eukaryotes

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]