Fig. 1.

Evolution of the photosensory GAF domain of phytochromes and CBCRs. (A) A topology diagram of the GAF domain, with the conserved “first Cys” and the three types of “second Cys” indicated. The first, second, fifth, and sixth beta strands are color-coded to match the sequence alignment in Fig. S3. (B) A neighbor-joining tree is shown for the GAF domains of published CBCRs and proteins described in this study, with names color-coded by ground-state absorbance. Branches with bootstrap values below 67% are indicated with an asterisk. Domains in parentheses bind bilin, but are photochemically inert (25). (C) Domain cartoons are shown for the proteins described in this work. CBCRs are color-coded by their photocycles, with near-UV absorbance represented by deep purple. Dashed GAF domains contain the first Cys, but have not yet been described.