Bacterial photoreceptor with similarity to photoactive yellow protein and plant phytochromes

A phytochrome-like protein called Ppr was discovered in the purple photosyn thetic bacterium Rhodospirillum centenum, Ppr has a photoactive yellow prot ein (PYP) amino-terminal domain, a central domain with similarity to phytoc hrome, and a carboxyl-terminal histidine kinase domain. Reconstitution expe riments demonstrate that Ppr covalently attaches the blue light-absorbing c hromophore p-hydroxycinnamic acid and that it has a photocycle that is spec trally similar to, but kinetically slower than, that of PYP. Ppr also regul ates chalcone synthase gene expression in response to blue light with autop hosphorylation inhibited in vitro by blue light. Phylogenetic analysis demo nstrates that R. centenum Ppr may be ancestral to cyanobacterial and plant phytochromes.