FIG. 1.

Schematic view of HIV-1 genome and transcripts produced during HIV-1 replication cycle (modified from reference 5 with permission). The ENF target region encompassing the amino acids 36 to 45 in gp41 is also shown. During the HIV-1 replication cycle, three classes of viral RNAs are produced: (i) the 9-kb unspliced mRNAs that are packaged into progeny virions as genomic RNA and can also serve for the expression of Gag/Pol genes; (ii) the singly spliced mRNAs encoding Vif, Vpr, Vpu, and env; and (iii) doubly spliced 2-kb transcripts encoding Tat, Rev, and Nef (29). The doubly spliced mRNAs encoding Tat, Rev, and Nef are the first produced and are transported into the cytoplasm by the ordinary cell machinery. When regulatory protein Rev is produced, it returns into the nucleus and binds the RRE, thus allowing the shuttling of unspliced and singly spliced mRNAs from the nucleus to the cytoplasm of HIV-1-infected cells.