Figure 9.

Proposed model of HIV-1 Gag association with USvRNA during transcription. (A) Our results demonstrate that treatment of HeLa HIV.Gag-GFP rtTA cells with Act D or DRB caused Gag to accumulate on USvRNAs that may be at or near transcription sites (orange box). Because Rev also binds USvRNA co-transcriptionally, there is a possibility that both Gag and Rev associate with USvRNA at transcription sites. Nuclear export of USvRNA was inhibited by LMB (purple box), along with small increase in HIV-1 Gag-GFP nuclear foci, yet there was no change in the degree of Gag-USvRNA co-localization. This finding suggests that there is a narrow “window of opportunity” for Gag-USvRNA to form vRNP complexes, starting at transcription but ending prior to formation of the export complex. (B) The model proposes that Gag binds to the 5′UTR psi sequence as it emerges during transcription. With transcription inhibition, Gag accumulates on stalled transcription complexes leading to an increase in Gag-USvRNA co-localization, potentially through additional Gag-Gag or Gag-RNA interactions.