The Evolution of DNA and Viruses

The Origin and Evolution of DNA and DNA Replication: A Review

• DNA is a modified form of RNA, with a stabilized backbone and the letter T replacing uracil.

• The first step in the emergence of DNA was most likely the formation of U-DNA (DNA containing uracil).

• Thymidylate synthase activity was invented twice independently, indicating that T-DNA might have appeared twice.

• The origin of DNA required the appearance of enzymes able to incorporate dNTPs using first RNA templates (reverse transcriptases) and later on DNA templates (DNA polymerases).

• The sense of DNA synthesis is a relic of the RNA world metabolism, as both purine and pyrimidine biosyntheses are built up on ribose 5 monophosphate as a common precursor.

• The origin and evolution of DNA replication mechanisms occurred at a critical period of life evolution that encompasses the late RNA world and the emergence of the Last Universal Cellular Ancestor (LUCA) to the present three domains of life.

• The traditional explanation for the selection of DNA as genetic material is that it is more stable and can be repaired more faithfully.

• Recent proposals suggest that viruses have played a major role in the origin and evolution of the DNA replication proteins and possibly of DNA itself.

• It has been proposed that U-DNA first appeared in a virus, making this first U-DNA organism resistant to the RNAses of its host.

• If DNA replication and repair mechanisms also originated in viruses, it is easy to imagine that enzymes to correct cytosine deamination are of viral origin and were later on transferred to cells.

• The idea that viruses have played a critical role in the origin of DNA is in line with previous conceptions that retroviruses were relics of the RNA/DNA world transition.

• The hypothesis of a viral origin for DNA could explain why many DNA viruses encode their own ribonucleotide reductase and/or thymidylate synthase.The Origin of DNA and Viruses

• Enzymes involved in viral DNA replication are often different from their cellular counterparts.

• Speculations suggest that viruses may have originated before the divergence between the three domains of life.

• Viruses are no longer considered fragments of genetic materials recently escaped from their hosts.

• Viruses are considered ancient players in life evolution.

• The discovery of structural and/or functional similarities between viruses infecting different cellular domains of life supports the idea that viruses originated before LUCA.

• Archaeal viruses (Lipothrixvirus and Rudivirus) have structural and/or functional similarities with several large eukaryal DNA viruses (Poxviruses, ASFV, Chlorella viruses).

• Adenoviruses (eukaryal virus) have structural and/or functional similarities with bacterial Tectiviruses.

• Eukaryal Flavivirus has structural and/or functional similarities with bacterial Cystoviruses.

• The discovery of these similarities supports the idea that viruses have ancient origins.

• The origin of DNA is still a mystery, and various theories have been proposed.

• One theory suggests that DNA may have originated from RNA, while another suggests that it may have originated from an ancient virus.

• The idea that viruses may have played a role in the origin of DNA is supported by the fact that enzymes involved in viral DNA replication are often very different from their cellular counterparts.

The Origin and Evolution of DNA and DNA Replication: A Review

• DNA is a modified form of RNA, with a stabilized backbone and the letter T replacing uracil.

• The first step in the emergence of DNA was most likely the formation of U-DNA (DNA containing uracil).

• Thymidylate synthase activity was invented twice independently, indicating that T-DNA might have appeared twice.

• The origin of DNA required the appearance of enzymes able to incorporate dNTPs using first RNA templates (reverse transcriptases) and later on DNA templates (DNA polymerases).

• The sense of DNA synthesis is a relic of the RNA world metabolism, as both purine and pyrimidine biosyntheses are built up on ribose 5 monophosphate as a common precursor.

• The origin and evolution of DNA replication mechanisms occurred at a critical period of life evolution that encompasses the late RNA world and the emergence of the Last Universal Cellular Ancestor (LUCA) to the present three domains of life.

• The traditional explanation for the selection of DNA as genetic material is that it is more stable and can be repaired more faithfully.

• Recent proposals suggest that viruses have played a major role in the origin and evolution of the DNA replication proteins and possibly of DNA itself.

• It has been proposed that U-DNA first appeared in a virus, making this first U-DNA organism resistant to the RNAses of its host.

• If DNA replication and repair mechanisms also originated in viruses, it is easy to imagine that enzymes to correct cytosine deamination are of viral origin and were later on transferred to cells.

• The idea that viruses have played a critical role in the origin of DNA is in line with previous conceptions that retroviruses were relics of the RNA/DNA world transition.

• The hypothesis of a viral origin for DNA could explain why many DNA viruses encode their own ribonucleotide reductase and/or thymidylate synthase.The Origin of DNA and Viruses

• Enzymes involved in viral DNA replication are often different from their cellular counterparts.

• Speculations suggest that viruses may have originated before the divergence between the three domains of life.

• Viruses are no longer considered fragments of genetic materials recently escaped from their hosts.

• Viruses are considered ancient players in life evolution.

• The discovery of structural and/or functional similarities between viruses infecting different cellular domains of life supports the idea that viruses originated before LUCA.

• Archaeal viruses (Lipothrixvirus and Rudivirus) have structural and/or functional similarities with several large eukaryal DNA viruses (Poxviruses, ASFV, Chlorella viruses).

• Adenoviruses (eukaryal virus) have structural and/or functional similarities with bacterial Tectiviruses.

• Eukaryal Flavivirus has structural and/or functional similarities with bacterial Cystoviruses.

• The discovery of these similarities supports the idea that viruses have ancient origins.

• The origin of DNA is still a mystery, and various theories have been proposed.

• One theory suggests that DNA may have originated from RNA, while another suggests that it may have originated from an ancient virus.

• The idea that viruses may have played a role in the origin of DNA is supported by the fact that enzymes involved in viral DNA replication are often very different from their cellular counterparts.