Shown above is the RNP complex formed by HIV-1 REV binding to the RRE upon mRNA of the env gene. Highlighted in slate is the ARM of the RNA binding domain, while colored in green is the mRNA with secondary stem-loop-like structure (PDB 4PMI).
Rev is a transactivating protein that is essential to the regulation of HIV-1 (and other lentiviral) protein expression. A nuclear localization signal is encoded in the rev gene, which allows the Rev protein to be localized to the nucleus, where it is involved in the export of unspliced and incompletely spliced mRNAs. In the absence of Rev, mRNAs of the HIV-1 late (structural) genes are retained in the nucleus, preventing their translation.