Figure 5.

The S-turn structure. Both A4318 and G4319 have C2′-endo sugar puckers. Recognition opportunities abound in the S-turn: G4319 is unstacked on its 5′-side; the furanose ring of G4319 is flipped exposing its hydrophobic backside, which together with the accessible and adjacent C8 and C5 atoms creates a hydrophobic pocket; and the phosphates of U4316, C4317, and G4319 create a notch in the backbone ridge.