The activity of the HIV-1 IRES is stimulated by oxidative stress and controlled by a negative regulatory element

Gendron, Karine; Ferbeyre, Gerardo; Heveker, Nikolaus; Brakier-Gingras, Léa

We investigated which are the regions of the 5 0 UTR of HIV-1 that are important for the IRES activity. Two deletion mutants were constructed. In mutant M1.Áloop202-217, 16 nt in the unstructured loop portion following the PBS were deleted while in mutant M2.ÁSL134-178, the irregular stem-loop encompassing nt 134-178, which has no known function to date, was deleted. The IRES activity was decreased to 39 ± 6% of the wild-type IRES activity with M1.Áloop202-217, but increased to 160 ± 8% with M2.ÁSL134-178 (Figure 2A) . These results suggest that the region encompassing nt 202-217 contains a positive determinant of the 5 0 UTR IRES activity. In contrast, the 134-178 stem-loop acts as a negative determinant of this IRES activity and was named IRENE (for IRES negative element). Both regions are highly conserved among group M subtype B natural variants (see Supplementary Results section and Supplementary Figures S1A and B) .