Prokaryotes-eukaryotes, common ancestor

However, the common view that archaebacteria were the hosts or directly ancestral to eukaryotes (Martin and Muller 1998 Van Valen and Maiorana 1980) is almost certainly mistaken. Instead I consider that eukaryotes are sisters to archaebacteria and that they diverged from a prokaryotic common ancestor after it acquired about 20 major novel properties not found in eubacteria (Cavalier-Smith 2002a). As these common properties include... 

Redundancy is seen when cells have available more than one protein for the same function. In such a situation, during evolution, one of the proteins - and the corresponding DNA - can be co-opted for another function. For instance, the prokaryotic protein FtsA and the eukaryotic protein actin are believed to be derived from a common ancestor. Both bind ATP but, in spite of structural similarity, are only 20% identical in sequence.24 They... 

Plastocyanins are the most widely studied cupredoxins. They are one of the most abundant copper proteins in plant photosynthetic tissues. Plant plastocyanins have an intricate evolutionary history because of their ancient bacterial origin. It is currently well accepted that plants diverged from the main eukaryotic domain into a separate lineage when the unicellular, oxygen respiring common ancestor of the eukaryotes incorporated a prokaryotic endosymbiont, the cyanobacterial chloroplast. 

In this view, the eukaryotes may well preserve some very primitive characteristics that are not seen in prokaryotes. Glansdorff (2000) reappraised claims for lateral gene transfer and concluded that the extent of transfer was overemphasized moreover, Glansdorff inferred that the last common ancestor was probably nonthermophilic and perhaps a protoeukaryote, from which the thermophilic archaea may have been the first divergent branch. 

As for the antiquity of the Eucarya there is no consensus. Those who support a eukaryote-like last common ancestor, of course, propose that the eukaryotes date to the very start of the Archean and end of the Hadean. It is not improbable to those who consider that the Eucarya were the last domain to appear, that Eukaryotes first evolved in the Archean aeon. There is, however, little support in the rock record for the hypothesis of a very late origin of both the archaea and eukaryotes, proposed by Cavaher-Smith (2002), especially as the evidence for early methanogens is strong (Grassineau et al., 2002 Rye and Holland, 2000). However, a proterozoic origin of the eukaryotes is not yet excluded, as the sterols found by Brocks et al. (1994) could be of prokaryote origin. 

Gu, X. (1997) The age of the common ancestor of eukaryotes and prokaryotes statistical inferences . Molecular Biology and Evolution, 14, 861-6. 

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