Schematic overview of the HIV-1 replication cycle in presence or absence of integrase inhibitors. The figure illustrates the main steps in the HIV-1 life cycle divided into an early and a late phase. The early phase includes: the attachment of the virus particle to the CD4 receptor and co-receptors CCR5 or CXCR4; the fusion with the host cell membrane; the uncoating of the viral capsid; the release of the HIV-1 RNA genome and proteins into the cytoplasm; the reverse transcription of the viral RNA genome into a DNA duplex, which has terminal duplications known as long terminal repeats (LTRs); the translocation into the nucleus and the integration into the cell genome. In the nucleus, unintegrated viral DNA is found in both linear and circular forms. The unintegrated circular forms of viral DNA have either one or two LTRs. The linear unintegrated viral DNA is the precursor of integrated proviral DNA, which is a stable structure that remains indefinitely in the host-cell genome. After the integration, the late phase of the cycle starts in which: the proviral DNA is transcribed to form new viral RNA, which subsequently is translated to form viral proteins; these proteins translocate to the cell surface to assemble in the cell membrane and form new viruses. Finally, the new viral particles bud off and are released as mature virions.