Monday, January 16, 2006

Did viruses invent DNA, enabling them to invade the earliest RNA-containing cells?

On January 12, 2006, the editor of the science journal, Nature, introduced a “News Feature” in the journal that reported on the idea of evolutionary biologist Patrick Forterre (University of Paris-Sud, Orsay) that viruses “…invented DNA as a way around the defences of the [RNA] cells they infected.”

The editor’s note, entitled, “War of the worlds”, referring to the RNA and DNA worlds, reads:

“In life's early days, most biologists believe, there was no DNA; instead, life stored its information in RNA, a versatile molecule that can also act as an enzyme. So how did DNA eventually take over this 'RNA world'?

“Evolutionary biologist Patrick Forterre suggests that viruses, not cells, triggered the change, adopting DNA not because of its merits as an information store but because it allowed them to evade the defences of RNA-based cells. The rest is evolutionary history.”

John Whitfield, a freelance science writer. wrote the “News Feature”, entitled “Origins of DNA: Base Invaders”, Nature 439, 130-131 (12 Jan 2006) doi: 10:1038/439130a.

You can find Forterre’s original article, “The two ages of the RNA world, and the transition to the DNA world: a story of viruses and cells”, in the journal, Biochimie, Vol. 87, pgs. 793-803, 2005

doi: 10.1016/j.biochi.2005.03.015

The Abstract of Forterre’s article reads (paragraphing added for ease of reading):

“Most evolutionists agree to consider that our present RNA/DNA/protein world has originated from a simpler world in which RNA played both the role of catalyst and genetic material. Recent findings from structural studies and comparative genomics now allow to get a clearer picture of this transition. These data suggest that evolution occurred in several steps, first from an RNA to an RNA/protein world (defining two ages of the RNA world) and finally to the present world based on DNA.

“The DNA world itself probably originated in two steps, first the U-DNA world, following the invention of ribonucleotide reductase, and later on the T-DNA world, with the independent invention of at least two thymidylate synthases. Recently, several authors have suggested that evolution from the RNA world up to the Last Universal Cellular Ancestor (LUCA) could have occurred before the invention of cells.

“On the contrary, I argue here that evolution of the RNA world taken place in a framework of competing cells and viruses (preys, predators and symbionts). I focus on the RNA-to-DNA transition and expand my previous hypothesis that viruses played a critical role in the emergence of DNA.

“The hypothesis that DNA and associated mechanisms (replication, repair, recombination) first evolved and diversified in a world of DNA viruses infecting RNA cells readily explains the existence of viral-encoded DNA transaction proteins without cellular homologues. It also potentially explains puzzling observations from comparative genomic, such as the existence of two non-homologous DNA replication machineries in the cellular world.

“I suggest here [in the article] a specific scenario for the transfer of DNA from viruses to cells and briefly explore the intriguing possibility that several independent transfers of this kind produced the two cell types (prokaryote/eukaryote) and the three cellular domains presently known (Archaea, Bacteria and Eukarya).”

TonySeb: Quite a story. Check out the “News Feature” and Forterre’s article.


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