Interplay between chromophore binding and domain assembly by the B-dependent photoreceptor protein, CarH.

Organisms across the natural world respond to their environment through the action of photoreceptor proteins. The vitamin B-dependent photoreceptor, CarH, is a bacterial transcriptional regulator that controls the biosynthesis of carotenoids to protect against photo-oxidative stress. The binding of B to CarH monomers in the dark results in the formation of a homo-tetramer that complexes with DNA; B photochemistry results in tetramer dissociation, releasing DNA for transcription.