Integration

Excerpt

Integration contributes to viral replication in two important ways. First, since retroviral DNA molecules are not ordinarily able to replicate autonomously as episomes, they depend on integration for stable maintenance in dividing cells. Once integrated, however, the provirus is replicated along with host-cell DNA and genetically transmitted as an integral element of the host genome. Integration also stabilizes the viral DNA against degradation: Unintegrated DNA molecules in an acutely infected cell are degraded by unknown processes within hours to days (Donehower and Varmus 1984; Kim et al. 1989; Pauza 1990; Roe et al. 1993; Barbosa et al. 1994; Pauza et al. 1994). Second, integration is important for efficient transcription of viral DNA into new copies of the viral genome and mRNAs that encode viral proteins. Thus, integration defines a turning point in the life cycle at which the virus can begin to multiply.