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As shown above left, this enzyme has an evolutionary tree extending back to LUCA confirming the obvious - that the genetic code cannot exist without the 21st software engineered amino acid selenocysteine!
In a ground-breaking project to identify genes that can illuminate the biology of LUCA, a team associated with Martin, (Weiss et al.
It is this tree which represents the climax fruitfulness of the biosphere and the genetic foundation of our existence, embracing not just higher Eucaryotes, plants, animals and fungi, but Protista, Eubacteria and Archaea, the realm, including the extreme heat and salt-loving organisms, which appears to lie almost at the root of life itself.
The notion of a tree of evolution veertically down te generations has become complicated by evidence for promiscuous horizontal gene transfer and for genetic symbiosis at the root of the eucaryote tree.
Genes meeting both criteria are unlikely to have undergone transdomain lateral gene transfer (LGT), and thus were probably present in LUCA and inherited within domains since then.
Similar considerations apply to ferredoxins, one of the most ancient coded proteins (Fitch & Bruschi 1987, Hall, Cammack & Rao 1974). To get a characterization of LUCA at the point it diversified into the three domains of life Archaea, Eucaryotes and Bacteria, one cannot rely on nucleotide gene sequences because these would have mutated beyond recognition, but amino acid sequences mutate more slowly because neutral mutations leave the amino acid sequence fixed and the tertiary folded structure of a protein is even more strongly conserved.
An ingenious piece of genetic software engineering evolved in which the amber stop codon UAG is overridden if the m-RNA possesses a motif called SECIS (selenocysteine insertion sequence).
Selenocysteine is then inserted instead of termination, and translation continues.
Fig 1b3: Evolutionary trees for two components of the electron transport chain, Fe-S proteins (left) and flavin-binding polypeptides (right archaea lower right Homo sapiens upper left), span the three domains of life (Schafer et al. It has also been proposed, on the basis of the highly-conserved commonality of transcription and translation proteins to all life, but the apparently independent emergence of distinct DNA replication enzymes in archaea/eucaryotes and eubacteria, that the last universal common ancestor had a mixed RNA-DNA metabolism based on reverse transcriptase, pinpointing it to the latter phases of the RNA era (Leipe et. The validity of the RNA-era concept and the capacity for RNAs to be both replicating informational and active ribo-enzymes is emphasized by the continuing dependence of the ribosome on r RNA rather than the protein components demonstrated by the 3D realizations of the two subunits in fig 1c1, which show that the r RNA molecules are still carrying out the central task of protein assembly with only minor modification due to the 'chaperoning' proteins, despite 3.8 billion years of evolution. (2002) have found that the amino acids used in sections of genes common to life which are believed to originate with LUCA show amino acid distributions reflecting the relative abundance of such amino acids in primitive synthesis, indicating that the first translational genes used the amino acids which were spontaneously available, consistent with my original hypothesis on origin of the genetic code in Biocosmology.
A specfic model of the evolution of the ribosome envisages that the smaller subunit which binds to and moves along the m RNA began first as an RNA-based RNA helicase which was essential to avoid the RNA era ending in non-replicating double stranded hairpins (Zenkin 2012).
2016) took a phylogenetic approach to decoding the LUCA metabolism.