Figure 8.

Schematic representation of peptide-induced RNA structural changes. (A) RNA only, (B) RNA in the presence of Tat(44–61) with its N-terminus in blue and its C-terminus in red. At low temperature, the interaction of the peptide with the RNA induces changes in the conformational equilibrium in a way that not only a single helical conformation is present but the helical-conformation is locally disrupted or partially melted. At intermediate temperatures (close to the ‘melting point’) the RNA is anyhow in a conformational equilibrium between helical and partially melted conformations. The addition of peptide to this pool of conformers results in a partial stabilization of the partially melted RNA conformations, which are probably the ones where RNA duplex formation initiates. At high temperatures, Tat(44–61) will stabilize not the completely randomized unfolded form of the RNA, but intermediates that are prone to interaction with a complementary strand of RNA.