FIGURE 8.

The tip of the tongue region of SynCph2. A, comparison of the photosensory modules of SynCph2 and SynCph1 at the tongue-GAF1 interface, color-coding corresponds to Fig. 7. B, the tongue region seals the PCB-binding pocket. In molecule B the whole tongue is defined by electron density. Only Arg³⁸³ of the PRXSF motif (spheres) is depicted as stick representation. Hydrogen bond distances are given in Å. C, chain A shows that the tip of the tongue is rather motile as several residues are missing and Arg³⁷³ adopts a different conformation.