When viruses were big…
Scientists have found evidence that viruses are living beings
Analysis of the first stages of the emergence of life on Earth has shown that viruses are not random fragments of DNA cells that have acquired an independent "life" by chance, but the product of the evolution of ancient cell-like structures adapted to intracellular parasitism, according to an article published in the journal Science Advances (Arshan Nasir and Gustavo Caetano-Anolles, A phylogenomic data-driven exploration of viral origins and evolution).
"Many organisms need other living things to survive, including bacteria living inside cells and parasitic fungi that are unable to complete the reproduction cycle without a host organism. The same thing, as it turns out, viruses do," said Gustavo Cayetano–Anolles from the University of Illinois at Urbana (in a press release, the University of Illinois Urbana-Champaign Study adds to evidence that viruses are alive – VM).
Cayetano-Anolles and his university colleague Arshan Nazir came to this conclusion by reconstructing the history of the very first steps of the evolution of life in the primary ocean of the Earth by how the shells of all viruses known to us differ.
As biologists explain, all viruses that exist today are protected from the external environment by a special protein shell, the so-called capsid, consisting of many separate repeating links. The structure of these "cubes", according to Cayetano-Anolles, is changing quite slowly, which makes it possible to reveal the history of the evolution of viruses by differences in genes containing instructions for assembling the capsid.
Guided by this idea, the authors of the article deciphered and compared the gene structures responsible for the assembly of such molecules in five thousand different strains of viruses, bacteria and multicellular creatures. Bacteria and multicellular organisms were included in this analysis for the reason that their genomes contain fragments of DNA from ancient retroviruses that disappeared hundreds of millions of years ago.
This comparison revealed two interesting and relatively unexpected things – scientists managed to find fragments of viral DNA that could not possibly be fragments of the genome of multicellular and bacteria, which many scientists considered involuntary "parents" of viruses. In addition to this, most viruses, judging by the similarities in the structure of capsid proteins, originate from one common ancestor.
"All this tells us that we can build a "tree of life" with the participation of viruses, since we have found many features in the structure of their genes that are related to their cells. In addition, they have their own unique components. This tree shows that viruses are descendants of several groups of ancient cells that coexisted with the ancestors of modern cells," Cayetano-Anolles continued.
Such a position of viruses on the tree of life allows us to say with confidence that they are not fragments of "rebellious" inanimate DNA that accidentally acquired the ability to infect other cells, but a special form of life that began to specialize in intracellular parasitism after one of the ancestors of viruses learned to protect their genetic code with the help of a capsid.
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28.09.2015