However, the latest arrival has completely upset commonly accepted ideas about the world of viruses. Dubbed Virophage, through analogy with bacteriophages that are bacteria virus, it was discovered in a giant virus called Mamavirus. The team of the Research Unit on Emerging Tropical and Infectious Diseases (CNRS/Aix Marseilles 2 University) headed by Didier Raoult has shown that the newcomer is also able to infect Mimivirus, a giant virus. Discovered by the team in 2003, Mimivirus is the largest virus with DNA ever identified. Until now, it is agreed that the three groups of living things (eukaryotes, bacteria and archaea) have parasite viruses special to each.
The team initially thought that the virophage was comparable to fragments of nucleic acids called satellites that are regularly associated with virus, hence the name Sputnik. However Didier Raoult and his team finally showed that it was an authentic virus. The virophage, which is unable to replicate alone in cells, has to replicate in the Mimivirus virus factory where it is churned out at the same time as its host. As a parasite of the Mimivirus, Sputnik causes a decrease of Mimivirus replication and 'manufacturing' defects characterized by morphological anomalies.
The virophage exchanges genes with Mimivirus, but it also imports virus genes from other living things. The analysis of its genome, conducted jointly with French and US researchers, has shown this. For instance, the scientists have discovered a very special gene composition in Sputnik: Mimivirus genes, an archaea virus gene, and two genes close to bacteriophage genes. Thus the virophage, a new viral family and new biological entity, is the virus of viruses that enables the performance of horizontal gene transfer between giant viruses. This discovery tends to confirm the idea that giant viruses, like other organisms, have viral parasites that are likely to help transfer genes from one virus to another.
Research results have just been published in the August 7, 2008 issue of Nature.
Research Unit on Emerging Tropical and Infectious Diseases - Unité de recherche sur les Maladies Infectieuses et Tropicales Emergentes (CNRS/Aix Marseilles 2 University) - Didier Raoult - Phone: +33 (0)4 91 32 43 75 - email: didier.raoult@medecine.univ.mrs.fr
