The late phase of the HIV-1 life cycle includes the regulated expression of the HIV gene products and the assembly of viral particles. The assembly of viral particles will be covered in a later release of Reactome. HIV-1 gene expression is regulated by both cellular and viral proteins. Although the initial activation of the HIV-1 transcription is facilitated by cellular transcription factors including NF-kappa B (Nabel and Baltimore, 1987), this activation results in the production of primarily short transcripts (Kao et al., 1987). Expression of high levels of the full length HIV-1 transcript requires the function of the HIV-1 Tat protein which promotes elongation of the HIV-1 transcript (reviewed in Karn, 1999; Taube et al. 1999; Liou et al., 2004; Barboric and Peterlin 2005). The HIV-1 Rev protein is required post-transcriptionally for the expression of the late genes. Rev functions by promoting the nuclear export of unspliced and partially spliced transcripts that encode the major structural proteins Gag, Pol and Env, and the majority of the accessory proteins (Malim et al., 1989; reviewed in Pollard and Malim 1998 .