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

From: The origin and early evolution of eukaryotes in the light of phylogenomics

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]