Table 6.4Extreme divergence between some essential eukaryotic proteins and their apparent prokaryotic orthologs

Phyletic pattern
Eukaryotic protein, function Bacterial ortholog, function Archaeal ortholog, function Probable evolutionary scenario Domain organization, Other comments and references
Actin, major cytoskeleton componentFtsA/MreB, cell division. All except mycobacteria and Synechocystis. MreB, cell division. Only Archaeoglobus, two methanogens and thermoplasmas.HGT from an endosymbiont to protoeukaryotes.HSP70-like ATPases [106,210,864,865].
Tubulin, major cytoskeleton componentFtsZ, cell division. All except chlamydia and Ureaplasma. FtsZ, cell division. All Euryarchaeota.Vertical inheritance from LUCA according to the standard model.Distinct GTPase domain [214,215,621].
LC7, small subunit of the dynein motor.MglB, implicated in GTPase regulation for signal transduction and gliding motility. Sporadic distribution.MglB, implicated in GTPase regulation for signal transduction. Sporadic distribution.Possible origin in the common archaeo-eukaryotic ancestor; additional HGTs.[455]
Separase (separin), protease responsible for chromatid separation in mitosis and meiosisHetF, heterocyst formation regulator in Cyanobacteria; Cyanobacteria, Streptomyces, Caulobacter. None.HGT from an endosymbiont to protoeukaryotes.The caspase- hemoglobinase protease domain [47,860].
Ddi1, predicted aspartic protease, cell cycle controlUncharacterized protein in alpha-proteobacteria.None.HGT from promitochondrial endosymbiont.Might be the progenitor of retroviral proteases [87,475].
Ubiquitin, the central mediator of controlled protein degradationMoaD, ThiS, Molybdenum cofactor and thiamin biosynthesis proteins. Most bacteria except for some parasites.MoaD, ThiS. All except Aeropyrum. Vertical inheritance from LUCA according to the standard model.[486]
DNA polymerase small subunitNone.All euryarchaeota.Vertical inheritance from archaeal ancestor.The archaeal ortholog is predicted to be an active phosphatase; the eukaryotic protein is inactivated leading to low sequence conservation [41].
ERCC4, the nuclease required for DNA incision in various forms of repairNone.All euryarchaeota.Vertical inheritance from archaeal ancestor.The archaeal ortholog is predicted to be an active helicase, but the eukaryotic protein is inactivated leading to low sequence conservation [54].

From: Chapter 6, Comparative Genomics and New Evolutionary Biology

Cover of Sequence - Evolution - Function
Sequence - Evolution - Function: Computational Approaches in Comparative Genomics.
Koonin EV, Galperin MY.
Boston: Kluwer Academic; 2003.
Copyright © 2003, Kluwer Academic.

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