title: Poxviruses and the origin of the eukaryotic nucleus.
abstract: A number of molecular forms of DNA polymerases have been reported to be involved in eukaryotic nuclear DNA replication, with contributions from alpha-, delta-, and epsilon-polymerases. It has been reported that delta-polymerase possessed a central role in DNA replication in archaea, whose ancestry are thought to be closely related to the ancestor of eukaryotes. Indeed, in vitro experiment shown here suggests that delta-polymerase has the potential ability to start DNA synthesis immediately after RNA primer synthesis. Therefore, the question arises, where did the alpha-polymerase come from? Phylogenetic analysis based on the nucleotide sequence of several conserved regions reveals that two poxviruses, vaccinia and variola viruses, have polymerases similar to eukaryotic alpha-polymerase rather than delta-polymerase, while adenovirus, herpes family viruses, and archaeotes have eukaryotic delta-like polymerases, suggesting that the eukaryotic alpha-polymerase gene is derived from a poxvirus-like organism, which had some eukaryote-like characteristics. Furthermore, the poxvirus's proliferation independent from the host-cell nucleus suggests the possibility that this virus could infect non-nucleated cells, such as ancestral eukaryotes. I wish to propose here a new hypothesis for the origin of the eukaryotic nucleus, posing symbiotic contact of an orthopoxvirus ancestor with an archaebacterium, whose genome already had a delta-like polymerase gene.
authors.affiliation: Laboratory of Cancer Cell Biology, Research Institute for Disease Mechanism and Control, Nagoya University School of Medicine, Tsurumai-cho 65, Showa-ku, Nagoya 466-8550 Japan. takemura@tsuru.med.nagoya-u.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Takemura
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D002467:Cell Nucleus / Q000201:enzymology / Q000382:microbiology / Q000502:physiology* / Q000821:virology; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D004261:DNA Replication; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004705:Endocytosis; D005057:Eukaryotic Cells / Q000166:cytology* / Q000201:enzymology / Q000821:virology; D019143:Evolution, Molecular; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D010802:Phylogeny; D011212:Poxviridae / Q000201:enzymology / Q000502:physiology*; D011387:Prokaryotic Cells / Q000166:cytology / Q000502:physiology / Q000821:virology; D017434:Protein Structure, Tertiary; D012313:RNA / Q000096:biosynthesis / Q000235:genetics; D013559:Symbiosis
chemical_list: D012313:RNA; D004247:DNA; D004259:DNA-Directed DNA Polymerase