The main function of IN is to insert the viral DNA into the host chromosomal DNA, a step that is essential for HIV replication. Integration is a "point of no return" for the cell, which becomes a permanent carrier of the viral genome (provirus). Integration is in part responsible for the persistence of retroviral infections. After integration, the viral gene expression and particle production may take place immediately or at some point in the future, the timing of which depends on the activity of the chromosomal locus hosting the provirus.