Four base triples produce uninterrupted base stacking between P1 and P2. (A) Network of hydrogen-bonding interactions (black dashes) of the four base triples spanning the P1–P2 junction. Only water molecules bridging nucleobases are shown. Alternate conformers of G13538 and G13539 are light blue. (B) Axial view of the G13486•C13492•G13538 triple. Blue mesh shows a portion of the 2|Fo|–|Fc| simulated annealing-omit map contoured at 1σ. Hydrogen-bonding distances (Å) are indicated. (C) Axial view of the U13485•G13493•A13537 triple. The ribose of U13494 (whose base is extruded into solvent) extends the hydrogen-bonding network. (D) Axial view of the G13484•C13495•C13536 triple. The phosphate of U13494 extends the hydrogen-bonding network. (E) Axial view of the A13483•U13496•A13535 triple.
