Escorts unspliced or incompletely spliced viral pre-mRNAs (late transcripts) out of the nucleus of infected cells. These pre-mRNAs carry two recognition sequences that function as Rev responsive element (RRE), that are not present in fully spliced viral mRNAs (early transcripts). This function is essential since most viral proteins are translated from unspliced or partially spliced pre-mRNAs which cannot exit the nucleus by the pathway used by fully processed cellular mRNAs (By similarity). Homomultimer; when bound to the RRE. Multimeric assembly is essential for activity (By similarity). The presence of both nuclear import and nuclear export signals leads to continuous shuttling between the nucleus and cytoplasm. The bipartite RNA-binding motif binds to the RREs present in incompletely spliced viral pre-mRNAs. It consists of a central region, and a C-terminal region that also contains the NLS which mediates nuclear localization. These overlapping functions prevent Rev bound to RRE from undesirable return to the nucleus. When Rev binds the RRE, the NLS becomes masked while the NES remains accessible (By similarity).