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

Deleting the 202-217 portion of the PBS loop or mutating the 240-242 bulge of the DIS hairpin or the 302-305 portion of loop I could remove the binding site for an unknown cellular factor whose binding stimulates the IRES activity, or could result in a conformational change that promotes a less active IRES conformation. The mutated/deleted nt in all these three mutants are very reactive according to Wilkinson et al. (31) , which implies that they are well exposed and free to interact with a factor. We observed that mutating the nt opposite to the 240-242 bulge in the DIS hairpin or mutating the last 2 nt of loop I did not change the IRES activity. This suggests that the decrease in the IRES activity obtained when nt 240-242 or 302-305 are mutated rather results from an effect localized to a welldefined region of the IRES than from a conformational change in the DIS hairpin or in loop I. It thus favors the possibility that nt 240-242 and 302-305 could be parts of the binding site for an ITAF. For the mutant with the deleted PBS loop, both a conformational change and the loss of the binding site for an ITAF could influence the IRES activity.