Bacteriophytochromes: Phytochrome-like photoreceptors from nonphotosynthetic eubacteria

Phytochromes are a family of photoreceptors used by green plants to entrain their development to the light environment. The distribution of these chro moproteins has been expanded beyond photoautotrophs with the discovery of p hytochrome-like proteins in the nonphotosynthetic eubacteria Deinococcus ra diodurans and Pseudomonas aeruginosa. Like plant phytochromes, the D. radio durans receptor covalently binds Linear tetrapyrroles autocatalytically to generate a photochromic holoprotein. However, the attachment site is distin ct, using a histidine to potentially form a Schiff base Linkage. Sequence h omology and mutational analysis suggest that D. radiodurans bacteriophytoch rome functions as a Light-regulated histidine kinase, which helps protect t he bacterium from visible Light.