Figure 2.

HIV-1 5′UTR IRES activity is modulated by two RNA regions. (A) Two deletion mutations, represented in the Weeks conformation, were made in HIV-1 5′UTR IRES and their effect on the IRES activity is shown. (B) Mutations of the upper part of the stem-loop 134–178, named IRENE, increase the IRES activity. The mutations are indicated in boxes. Note that this figure describes the mutations that were introduced but not the structure adopted by the mutant stem-loops (see Figure 5). (C) Replacement of the 3A bulge of IRENE by 3C or 3U but not by 3G increases the IRES efficiency. The IRES activities for the mutants were assessed in lysates from Jurkat T cells transfected with the corresponding dual-luciferase plasmids. The Fluc/Rluc ratio obtained with the wild-type pFRT-dual-IRES-HIV (WT) was arbitrarily set at 100%. Results are the mean ± SEM of six independent experiments. The asterisk indicates mutants that were significantly different from WT (P < 0.05).