Figure 1.

Motifs in the HIV-1 RNA genome that regulate reverse transcription. (A) The HIV-1 DNA genome is shown with the nine open reading frames. The untranslated leader encoding multiple regulatory elements is schematically depicted. A 3′-nested set of transcripts used as template for reverse transcription initiation are shown with the PAS and PBS motifs. (B) Alternative structures of the HIV-1 leader RNA. The ground state conformation contains a long-distance interaction (LDI) between the polyA and DIS domains. The alternate conformation exposes the polyA and DIS hairpins and takes the form of a branched structure (BMH). (C) Model of PAS-mediated tRNA primer activation. First, the tRNA^lys3 primer anneals to the PBS (indicated in blue), subsequently the anti-PAS sequence in tRNA^lys3 must anneal to the PAS (purple) before efficient reverse transcription initiation can take place.