Schematics of the retroviral replication cycle. This figure illustrates the pathway of a retrovirus during infection of a susceptible host cell. Note the processes of (1) viral attachment to a specific receptor, (2) viral entry, (3) viral reverse transcription, (4) nuclear entry of double-stranded viral DNA, (5) viral integration into host genome, (6) viral genomic replication, (7) viral packaging and (8) budding and exit. Note that the scalars and tensors in figure 2 act at any of these steps. Source Citation .