Eukaryotes ancestors 273

The distance between the two bacterial kingdoms is comparable to the distance that divides each of them from the eukaryotes ancestors (cells that Woese called urkaryotes). 

Table Xl/I High mobility group (HMG) proteins of unicellular eukaryotic ancestors become onco Ht)teins in human cancer cells. 1 Introduction...

Mitochondria were already present in the primitive eukaryotic ancestor when plastids were first acquired by symbiosis. 

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... 

Fig. 6.13 The development of aerobic eukaryotic organisms from the earliest anaerobic ancestors via aerobic bacteria, all single cells.

The family of eukaryotic Ras-like small GTPases may be divided into subfamilies, namely those of ARF, Rab, Ran, Ras, Rho, and Sar (ARF, RAB, RHO, RAS, RHO, SAR), which all contain representatives from fungi, plants, and metazoa. Consequently, these subfamilies and their cellular functions are likely to have emerged early in eukaryotic history. This implies that the last common ancestor of fungi, plants, and metazoa possessed vesicular transport (ARF and Sar), membrane trafficking (Rab), nuclear transport (Ran), signal transduction (Ras), and regulation of the actin cytoskeleton (Rho) functions. 

According to one favored theory, mitochondria evolved from aerobic bacteria that were endocytosed by an anaerobic ancestor of eukaryotic cells. The endocytic event is thought to have occurred when oxygen emerged in the atmosphere (about two billion years ago) and threatened most life systems. Under the selective pressure of oxygen, a stable relationship developed in which the host cell had acquired the ability to exploit the bacterial oxidative phosphorylation system for their own use (Green and... 

Margulis L, Chapman M, Guerrero R, Hall J (2006) The last eukaryotic common ancestor (LECA) Acquisition of cytoskeletal motility from aerotolerant spirochetes in the Proterozoic Eon. Proc Natl Acad Sci USA 103 13080-13085... 

The machinery mediating this process was shown to be of an ISC type. Phylogenetic analyses indicate that the mitochondrial ISC machinery was inherited from the proteobacterial endosymbiont, which is consistent with the proposed origin of mitochondria (Tachezy et al. 2001). Components of the SUF system were found in plastids and in the apicoplast of apicomplexan such as P. falciparum (Wilson et al. 2003). The SUF machinery was most likely inherited from cyanobacteria, the ancestors of plastids (Tachezy et al. 2001). Entamoebids and related protists are the only eukaryotes which acquired components of the NIF system ( et al. 2004 van der Giezen et al. 

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