Neomura

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LIFE
Linnaean taxonomy Phylogeny and hypothetical timeline (not to scale)
* Domain: Eubacteria
* Domain: Archaea
* Domain: Eukarya
** Kingdom: Plantae
** Kingdom: Fungi
** Kingdom: Metazoa 
Hadean  Archean  Proterozoic  Phanerozoic 
     LUCA
       |--Eubacteria ---------------------
       `--Archaea  -----------------------
            `---- Eukarya ----------------
                     |--Plantae  ---------
                     `-----+--Fungi ------
                           `--Metazoa ----

Life in the Universe: Definitions of life | Exobiology | Origin of life

Life on Earth: Biology | Ecology | Evolution | The Fossil record | Genetics | Physiology | Systematics


Neomura refers to a clade composed of the two domains of Archaea and Eukarya. The group was first proposed by Thomas Cavalier-Smith and its name means "new walls", so called because it was thought to have evolved from Eubacteria and one of the major changes was the replacement of peptidoglycan cell walls with other glycoproteins.

[edit] Morphology

As it contains both prokaryotic and eukaryotic members, the Neomura is a very diverse group, containing all multicellular organisms, as well as many of the most extremophilic species. Nevertheless, all neomurans share certain molecular characteristics. Most have histones to help with chromosome packaging, and most have introns. All use the molecule methionine as the initiator amino acid for protein synthesis (Eubacteria use formylmethionine). Finally, all neomurans use several kinds of RNA polymerase, whereas Eubacteria use only one.

[edit] History

A phylogenetic tree, showing how Eukaryota and Archaea are more closely related to each other than to Bacteria, based on Cavalier-Smith's theory of bacterial evolution.
A phylogenetic tree, showing how Eukaryota and Archaea are more closely related to each other than to Bacteria, based on Cavalier-Smith's theory of bacterial evolution.
When Carl Woese first published his three-domain system, it was believed that the domains Bacteria, Archaea, and Eukarya were equally old and equally related on the tree of life, but certain evidence began to suggest that Eukarya and Archaea were more closely related to each other than either was to Bacteria. This evidence included the common use of cholesterols and proteasomes, which are complex molecules not found in most bacteria. Recently, Cavalier-Smith showed evidence that Neomura evolved from Eubacteria. The strongest evidence is that all known eukaryotes have mitochondria, which almost certainly evolved through endosymbiosis with an alpha-proteobacteria (a highly evolved group of bacteria). If Eukarya is as old as Bacteria, it almost certainly would have branched during the many millions of years it took for Bacteria to evolve the aerobic respiration performed by mitochondria, and some eukaryotes would have evolved without mitochondria.

An smaller but important piece of evidence is that the cholesterols and proteasomes found in Neomura are also found in Actinobacteria. Molecules of this complexity are unlikely to evolve more than once in separate branches, so either there was a horizontal transfer of those two pathways, or Neomura evolved from this particular branch of the bacterial tree.

[edit] References

Cavalier-Smith, T. 1987. The origin of eukaryote and archaebacterial cells. Annals of the New York Academy of Sciences 503: 17–54.

Cavalier-Smith, T. 2002. The neomuran origin of archaebacteria, the negibacterial root of the universal tree and bacterial megaclassification. International Journal of Systematic and Evolutionary Microbiology 52: 7–76.

Cavalier-Smith, T. 2006. Rooting the tree of life by transition analyses. Biol Direct 1: 19.

Skophammer, R. G., J. A. Servin, C. W. Herbold & J. A. Lake. 2007. Evidence for a gram-positive, eubacterial root of the tree of life. Molecular Biology and Evolution 24 (8): 1761-1768.

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This page incorporates material from Wikipedia which is available under the terms of the GNU Free Documentation License. Wikipedia url for material on this page:
http://en.wikipedia.org/wiki/Neomura.
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