Poxviruses and the origin of the eukaryotic nucleus

A number of molecular forms of DNA polymerases have been reported to be inv olved in eukaryotic nuclear DNA replication, with contributions from alpha- , delta-, and epsilon -polymerases. It has been reported that delta -polyme rase possessed a central role in DNA replication in archaea, whose ancestry are thought to be closely related to the ancestor of eukaryotes. Indeed, i n vitro experiment shown here suggests that delta -polymerase has the poten tial 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 conserve d regions reveals that two poxviruses, vaccinia and variola viruses, have p olymerases similar to eukaryotic alpha -polymerase rather than delta -polym erase, while adenovirus, herpes family viruses, and archaeotes have eukaryo tic delta -like polymerases, suggesting that the eukaryotic alpha -polymera se 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 sym biotic contact of an orthopoxvirus ancestor with an archaebacterium, whose genome already had a delta -like polymerase gene.