Structure of the HIV-2 leader region. 1a. Secondary structure model of the HIV-2 leader region based on mfold predictions. Indicated are the putative dimer linkage sites (in red). Also highlighted is the DM region defined as being critical for packaging , in blue). 1b. The effect of the DM deletion on the SL1/DIS stem loop. The stem is truncated and the internal bulge altered in approximately half the predicted structures.