Figure 3. The common exon forms a similar structure in all HIV-1 transcripts. Quantitated, normalized, and background-corrected modification data from at least two independent SHAPE probing experiments. The relative SHAPE reactivity is on the y-axis and the defined RNA elements of the common exon are shown 5′ to 3′ on the x-axis (gray and white shading). RNA elements include the trans-activating region (TAR), the polyadenylation signal (poly (A)), the primer binding site (PBS), the dimerization initiation site (DIS), the major splice donor site (SD) and the packaging signal (PSI) and the leader specific sequences (289–336 nts).