The 1.2-Megabase Genome Sequence of Mimivirus

TLDR

Mimivirus is a double‑stranded DNA virus that replicates in amoebae. The study aims to use the new genome sequence to illuminate the origins of DNA viruses and their role in early eukaryotic evolution. The 1.18‑million‑base pair genome contains 1,262 ORFs, 10 % of which match known proteins, and encodes numerous translation, repair, and metabolic genes—including tRNAs and amino‑acyl tRNA synthetases—making it the largest and most complex virus known and blurring the line between viruses and parasitic cells.

Abstract

We recently reported the discovery and preliminary characterization of Mimivirus, the largest known virus, with a 400-nanometer particle size comparable to mycoplasma. Mimivirus is a double-stranded DNA virus growing in amoebae. We now present its 1,181,404–base pair genome sequence, consisting of 1262 putative open reading frames, 10% of which exhibit a similarity to proteins of known functions. In addition to exceptional genome size, Mimivirus exhibits many features that distinguish it from other nucleocytoplasmic large DNA viruses. The most unexpected is the presence of numerous genes encoding central protein-translation components, including four amino-acyl transfer RNA synthetases, peptide release factor 1, translation elongation factor EF-TU, and translation initiation factor 1. The genome also exhibits six tRNAs. Other notable features include the presence of both type I and type II topoisomerases, components of all DNA repair pathways, many polysaccharide synthesis enzymes, and one intein-containing gene. The size and complexity of the Mimivirus genome challenge the established frontier between viruses and parasitic cellular organisms. This new sequence data might help shed a new light on the origin of DNA viruses and their role in the early evolution of eukaryotes.