Figure 1.

Overall structure of the bacterial phytochrome from D. radiodurans. A, simplified domain composition of the full-length phytochrome. The biliverdin bound to the N-terminal extension of the PAS domain and the PHY tongue are depicted. B, crystal structures of the photosensory module in closed (Pr, blue) and open (Pfr, white) conformations (9). Tongue, conserved DIP and PRXSF motifs (green), Tyr²⁶³ (red), and the chromophore (orange) are indicated. The double-headed arrows represent the changes in the PHY domain separation upon illumination. The CBD part has been shown only for the Pr-state structure for clarity. HK, histidine kinase.