REV (116 amino acids)

REV alters the splicing of genomic viral RNA. In the presence of REV, unspliced RNA is directed away from cellular splicing enzymes by the promotion of export from the nucleus. At first, in the absence of REV, most RNA transcripts are doubly spliced to make the RNAs that encode TAT, REV and NEF (early proteins). With the exception of  NEF, these are not incorporated into the mature virion. Later, protein synthesis is switched to the formation of viral structural proteins, the mRNAs for which are either not spliced at all (gag/pol) or are singly spliced (env).

 Normally, cellular mRNAs are spliced before leaving the nucleus. The function of REV is to allow mRNAs that are not fully spliced to leave the nucleus. There is a region in the ENV gene called the rev-responsive element (RRE) that is important for this. It is a hairpin structure that binds several REV molecules. Note that the RRE is not in the mRNAs for TAT, REV and NEF because of splicing. Although how REV works is still debated, it seems to participate directly in RNA export of unspliced RNAs containing the RRE . NEF protein itself contains a nuclear export signal that is leucine-rich and appears to interact with proteins of the nuclear pore

For further information see: Alan Frankel and John A. T. Young, HIV-1: Fifteen proteins and an RNA Annual Review of Biochemistry 67: 1-25, 1998