Fig. 8.

The role of the K-turn in the architecture of the SAM-I riboswitch. Molecular graphic images as parallel-eye stereoscopic views.

A. Cartoon showing the structure of the complete riboswitch [4]. The K-turn (K) kinks the long helix so that its terminal loop (L) can interact with the receptor (R). This contributes to the fold of the riboswitch so that it can bind the S-adenosylmethione ligand (highlighted in magenta).

B and C show two more detailed views of the K-turn and the loop–receptor interaction, with the K-turn at the top. The terminal loop of the C helix of the K-turn (colored green) is basepaired with a remote section of the riboswitch (blue).