Purification and characterization of a recombinant bacteriophytochrome of Xanthomonas oryzae pathovar oryzae.

Phytochrome-like proteins have been recently identified in prokaryotes but their features and functions are not clear. We cloned a gene encoding the phytochrome-like protein (XoBphP) in a pathogenic bacteria, Xanthomonas oryzae pv. oryzae (Xoo) and investigated characteristics of the protein using a recombinant XoBphP. The N-terminal region of XoBphP containing the PAS/GAF/PHY domains is highly similar to most bacteriophytochromes, but Cys4, corresponding to Cys24 of DrBphP, isn't involved in chromophore attachment. Recombinant XoBphP could bind a bilin molecule and a differential spectrum from Pr/Pfr shows that XoBphP has similar characteristics of known bacteriophytochromes with shifted absorption maxima of 683 and 757 nm for the Pr and Pfr forms. Unlike other bacteriophytochromes, XoBphP has no histidine kinase domain at C-terminus. The domain was predicted from amino-acid 279 to 342 with less significance than the required threshold. This result suggests that XoBphP probably has different signal transduction mechanisms for its intracellular function.