Human immunodeficiency virus type 1 gag-pol frameshifting is dependent on downstream mRNA secondary structure: demonstration by expression in vivo.

The human immunodeficiency virus type 1 (HIV-1) Gag-Pol fusion polyprotein is produced via ribosomal frameshifting. Previous studies in vitro and in Saccharomyces cerevisiae have argued against a significant role for RNA secondary structure 3' of the shift site, in contrast with other systems, in which such structure has been shown to be required. Here we show, by expressing the HIV-1 gag-pol domain in cultured vertebrate cells, that a stem-loop structure 3' of the HIV-1 shift site is indeed important for wild-type levels of frameshifting in vivo.