Mimivirus, short for "mimicking microbe", is so called to reflect its large size and apparent Gram-staining properties.

In 2003, researchers at the Université de la Méditerranée in Marseille, France, published a paper in Science identifying the micro-organism as a virus.

[9] Mimivirus has been placed into a viral family by the International Committee on Taxonomy of Viruses as a member of the Mimiviridae,[10] and has been placed into Group I of the Baltimore classification system.

Variation in scientific literature renders these figures as highly approximate, with the "size" of the virion being casually listed as anywhere between 400 nm and 800 nm, depending on whether total length or capsid diameter is actually quoted.

[12] It does not appear to possess an outer viral envelope, suggesting that the virus does not exit the host cell by exocytosis.

[13] Mimivirus shares several morphological characteristics with all members of the NCLDV group of viruses.

The condensed central core of the virion appears as a dark region under the electron microscope.

However, three distinct aminoacyl tRNA synthetase enzyme transcripts and four unknown mRNA molecules specific to mimivirus were also found.

[13] The mimivirus genome is a linear, double-stranded molecule of DNA with 1,181,404 base pairs in length.

Once inside, an eclipse phase begins, in which the virus disappears and all appears normal within the cell.

[citation needed] These micrographs show mimivirus capsid assembly in the nucleus, acquisition of an inner lipid membrane via budding from the nucleus, and particles similar to those found in many other viruses, including all NCLDV members.