Examining the role of the DIS in copackaging of HIV-1 and HIV-2 RNA. (A) Predicted secondary structure of a portion of the 5′ leader sequences of HIV-1, containing stem-loop 1, stem-loop 2, and stem-loop 3 (labeled SL1, SL2, and SL3) (33). (B) Predicted secondary structure of a portion of the 5′ leader of HIV-2 containing stem-loop 1, stem-loop 2, and stem-loop 3 (labeled SL1, SL2, and SL3) (9). DIS, dimer initiation signal. Nucleotides that comprise the DIS are outlined. (C) General structures of HIV-1 constructs and their DIS sequences. The wild-type DIS sequence (GCGCGC) of HIV-1–gagCeFP-MS2SL is shown for comparison. (D) General structures of HIV-2 constructs and their DIS sequences. The wild-type HIV-2 DIS sequence (GGUACC) is shown as a reference.