Pandoravirus

Pandoravirus is a genus of very large viruses. They have the largest genomes of any viral genus. Like the other large viruses "Mimivirus", "Pithovirus" and "Megavirus", "Pandoravirus" infects amoebas. Its genome, with 1.9 to 2.5 megabases of DNA, is twice as large as that of "Megavirus". It differs greatly from the other large viruses in appearance and in genome structure.
Although the capsid of "Pithovirus" is 50% larger in size, "Pandoravirus" has the largest genome of all viruses (2.5 million base pairs).
About 93% of Pandoravirus genes are not known from any other microbes. This led some scientists to suggest the virus belongs to a "fourth domain", aside from Bacteria, Archaea, and Eukaryotes. Viruses as a whole are not considered to be within these three domains, but they have been proposed as one in the past by some biologists.