[Split]Viruses and Prions without God Wrath!
April 25, 2013 at 3:47 pm
(This post was last modified: April 25, 2013 at 3:49 pm by L.A.F..)
Patrick Forterre of the Institut Pasteur has suggested a novel evolutionary scenario for how cells obtained DNA that also explains how the cellular machinery that deals with DNA originated in viruses in the first place.
Forterre's hypothesis starts with an RNA world consisting of cells with RNA genomes plus viruses with RNA genomes. Viruses with DNA genomes were then selected because this protected them from degradation by cellular nucleases. This would have occurred before the LUCA (also containing an RNA genome) split into the three domains (Archaea, Bacteria, Eukarya).
Then three nonvirulent DNA viruses ("founder viruses") infected the ancestors of the three domains. The three DNA viruses replicated inside their host cells as DNA plasmids, much as a P1 prophage replicates inside Escherichia coli today. Furthermore, two of the founder viruses were more closely related to each other (and these infected the ancestors of today's Archaea and Eukarya) than to the third founder virus (which infected the ancestor of Bacteria). Gradually, cells converted their genes from RNA to DNA due to its greater stability. Reverse transcriptase is believed to be an enzyme of very ancient origin, and it is conceivable that it was involved in the convrsion of RNA genes to DNA, as occurs in retroviruses today.
(Madigan, M. et al. (2012), Brock Biology of Microorganisms, 13th Ed. Pearson Education, p. 276)
Although this hypothesis does not wholly explain the origin of viruses, it does explain their diversity of replication systems and the very ancient structural similarities between certain families of DNA and RNA viruses.
My knowledge of molecular biology is limited and I am thus unable to hypothesize about the origin of prions.
Forterre's hypothesis starts with an RNA world consisting of cells with RNA genomes plus viruses with RNA genomes. Viruses with DNA genomes were then selected because this protected them from degradation by cellular nucleases. This would have occurred before the LUCA (also containing an RNA genome) split into the three domains (Archaea, Bacteria, Eukarya).
Then three nonvirulent DNA viruses ("founder viruses") infected the ancestors of the three domains. The three DNA viruses replicated inside their host cells as DNA plasmids, much as a P1 prophage replicates inside Escherichia coli today. Furthermore, two of the founder viruses were more closely related to each other (and these infected the ancestors of today's Archaea and Eukarya) than to the third founder virus (which infected the ancestor of Bacteria). Gradually, cells converted their genes from RNA to DNA due to its greater stability. Reverse transcriptase is believed to be an enzyme of very ancient origin, and it is conceivable that it was involved in the convrsion of RNA genes to DNA, as occurs in retroviruses today.
(Madigan, M. et al. (2012), Brock Biology of Microorganisms, 13th Ed. Pearson Education, p. 276)
Although this hypothesis does not wholly explain the origin of viruses, it does explain their diversity of replication systems and the very ancient structural similarities between certain families of DNA and RNA viruses.
My knowledge of molecular biology is limited and I am thus unable to hypothesize about the origin of prions.
