In 2005, the Vierstra and Forest labs at the University of Wisconsin published a three-dimensional structure of a truncated "Deinococcus" phytochrome (PAS/GAF domains). This paper revealed that the protein chain forms a knot - a highly unusual structure for a protein. In 2008, two groups around Essen and Hughes in Germany and Yang and Moffat in the US published the three-dimensional structures of the entire photosensory domain. One structures was for the "Synechocystis sp. (strain PCC 6803)" phytochrome in Pr and the other one for the "Pseudomonas aeruginosa" phytochrome in the Pfr state. The structures showed that a conserved part of the PHY domain, the so-called PHY tongue, adopts different folds. In 2014 it was confirmed by Takala et al that the refolding occurs even for the same phytochrome (from "Deinococcus)" as a function of illumination conditions.