12 Feb , 18:15
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The Last Universal Common Ancestor of all modern organisms — LUCA (Last Universal Common Ancestor) — existed approximately 4.2 billion years ago. However, new research published in the journal Cell Genomics reveals a striking fact: some of its genes may have even more ancient origins and trace back to completely extinct forms of life.
Scientists turned to studying so-called universal paralogs — ancient duplicated genes that are present in all branches of life on Earth. It is precisely these genes that allow us to peer beyond LUCA and approach the very origins of evolution.
Universal paralogs are pairs of related genes that arose through duplication before life split into bacteria, archaea, and eukaryotes. If LUCA can be imagined as the trunk of the tree of life, then the organisms in which these duplicates first appeared are its roots. Such genes offer a unique opportunity to test hypotheses about the deepest stages of biological history.
Fossil evidence from that era has virtually not been preserved, so the genomes of modern organisms remain the primary source of knowledge about the distant past. At the same time, many ancient genes may have disappeared due to mutations, horizontal transfer, or loss of function. Only a small fraction of the original genetic heritage has survived to the present day.
"The history of these universal paralogs is the only information we will ever have about the earliest cellular lineages," the researchers emphasize.
Of particular interest to scientists were genes associated with the translation system — the mechanism of protein synthesis from genetic code. This system, by all appearances, is one of the most ancient molecular mechanisms that has survived to the present day.
Recent studies have demonstrated that precursors of aminoacyl-tRNA synthetase enzymes existed before LUCA. These enzymes ensure the attachment of the correct amino acid to the corresponding transfer RNA — a key step in protein formation.
"There aren't enough words to describe how important these enzymes are for life," the authors note. Their existence before LUCA indicates that early forms of life already possessed the ability to synthesize proteins from genetic code, albeit in a more primitive form.
