The gene's protein product allows fragments of HIV mRNA that contain a HIV Rev response element (RRE) to be exported from the nucleus to the cytoplasm.
In the absence of the rev gene, the hostRNA splicing machinery in the nucleus quickly splices the RNA so that only the regulatory proteins Rev and Tat and the accessory protein Nef can be produced. In the presence of rev, RNA is exported from the nucleus before it can be spliced, so that the structural proteins and RNA genome can be produced. This mechanism allows a positive feedback loop to allow HIV to overwhelm the host's defenses, and provides time-dependent regulation of replication.
The rev gene coding sequence is supplied in a separate plasmid along a with structural and functional gene-containing plasmid (gag-pol) for the safe production of HIV-1 in the laboratory for research purposes. Viral-like particle (VLP) production won't occur if this Rev plasmid is missing.