Figure 7

Schematic of the different short- and long-range RNA interactions that regulate lentiviral SL1-mediated dimerization. Three short- and long-range RNA structures can regulate SL1-mediated tight dimerization in HIV-2, SIV, and HIV-1. A. LDI (long-distance interaction) is an extensive, long-range base pairing interaction between the U5 and SL1 domains that causes a large rearrangement of the leader RNA structure [17]. SL1 is completely sequestered and thus unable to initiate dimerization. B. CGI (C-box – G-box interaction) is a long-range base pairing interaction between a sequence in U5 and the gag translation initiation region (called C-box and G-box, respectively). Formation of CGI impairs SL1-mediated dimerization in HIV-2 ([21, 25]), and favors it in HIV-1 [17]. C. Stem B is the lower stem of SL1 and has important roles during viral replication in HIV-1 ([43, 45]), HIV-2 ([6, 7]), and SIV ([50, 51]). Stem B-mediated SL1 entrapment may have twin roles in the regulation of lentiviral leader RNA dimerization since promoting SL1 presentation by increasing its folding stability (Table 3) may favor the formation of SL1 loop/loop (i.e. loose) dimers, while impairing the transition from loose to tight dimers.