Virophage Concept, The

Abstract The existence of small viruses that depend on the coinfection of their host cells by another virus has been known for a long time. These viruses are considered to be satellites of their helper viruses. The discovery of Sputnik, Mavirus and the Organic Lake virophage shook this vision of subviral agents. Indeed, these new viruses are not only dependent on coinfection but are also noxious for their so‐called host viruses, leading to sick particles. This surprising capability established the concept of a virophage, which is a virus infecting a virus. Studies on the morphology, life cycle and genomes of virophages have enriched this concept by highlighting unexpected features. Thus, the question of the classification of the virophages among the satellite viruses within the virosphere has been brought to light. Key Concepts: Virophages are small viruses discovered to be associated with the largest viruses of the virosphere. As satellite viruses, virophages are dependent on coinfection of their host cells with their host viruses. This coinfection results in the lysis of the cell, diminution of the production and infectivity of the host virus and an increase in the production of abnormal particles of the giant virus. The virophages may hijack the replication mechanisms of their host viruses within their host cells. Virophage replication occurs in the viral factory, a dense cytoplasmic region that appears a few hours after infection by the host virus with or without its virophage.