In vitro expression of the HIV-2 genomic RNA is controlled by three distinct internal ribosome entry segments that are regulated by the HIV protease and the Gag polyprotein.

The HIV-2 genomic RNA serves both as a messenger for protein synthesis and as a genome for viral assembly and particle production. Our previous work has shown that the HIV-2 genomic RNA encodes two additional Gag proteins that are N-terminal truncated isoforms of the p57 Gag polyprotein. In this study, by the use of mono- and bicistronic RNAs we show that translation at the three AUGs is driven by three distinct and independent internal ribosome entry segments both in vitro and ex vivo. Furthermore we used the recombinant Gag and HIV-2 protease to show that, in vitro, translation is tightly regulated by these two viral proteins. This regulation is exerted both at the level of protein production and also on the selection of the AUG initiation site which changes the ratio at which the three different Gag isoforms are produced.