Last universal common ancestor LUCA

The three domains of living organisms have been established by the analysis of the small-subunit rRNAs. Their comparison made it possible to divide the organisms into the three well-known kingdoms (Follmann and Brownson 2009 and Woese references cited therein). Besides rRNAs, tRNAs are among the most ancient molecules, and phylogenetic trees can be constructed from them that are not inconsistent with those constructed from rRNAs and from proteins. Keep in mind that these trees are not necessarily organismal trees. Thus, a last universal common ancestor, LUCA, was introduced (Follmann and Brownson 2009 and Woese references cited therein). The notion of LUCA is based on assumptions it is not a discrete entity. But extensive analyses have been carried out that seem to support the LUCA model. 

The catalytic domains of human 25 kDa hThTPase and CyaB-like adenylyl cyclase from Aeromonas hydrophilia define a novel superfamily of domains that should bind organic phosphates (Iyer and Aravind 2002). This superfamily of proteins was therefore called CYTH (CYaB-THiamin triphosphatase), and the presence of orthologs was demonstrated in all three superkingdoms of life. This suggested that CYTH is an ancient enzymatic domain and that a representative must have been present in the last universal common ancestor (LUCA) of all extant life forms. It appears that the CYTH superfamily includes enzymes with various catalytic properties (adenylyl cyclase or inorganic triphosphatase in some bacteria, RNA triphosphatase in yeast, ThTPase in animals) but with important common features ... 

The common root represents LUCA, the Last Universal Common Ancestor of bacteria, archaea and eukaryotes. Notice that the Archaea are intermediate between the Bacteria and Eucarya, as inferred from many of their detailed morphological and biochemical properties, as well as their ribosomal RNA sequences. The boxed dates indicate the minimum age of selected branches, based on fossil evidence and biochemical fingerprints, such as the characteristic membrane steroids found by Jochen Brocks and his colleagues in the shales underlying the Hammersley iron formation in Australia. Adapted with permission from Andrew Knoll and Science. 

LUCA (Last Universal Common Ancestor) the last... 

While the idea that life originated — and the first RNA and protein molecules evolved — in Zn -rich settings appears to be compatible with the available data, it does not explicitly state whether these Zn -rich settings played any direct role in the formation of the first cells. Although it is hard to make any specific and verifiable predictions for these matters, in this section we try tracing the possible roles of Zffi ions at the times of the Last Universal Common Ancestor of all living cellular organisms (LUCA). 

Mushegian A Gene content of LUCA, the last universal common ancestor. Front Biosci 2008, 13 4657-4666. 

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