Chromophore composition of a heterologously expressed BLUF-domain

Upon heterologous expression of the BLUF (for: Blue-Light sensing U sing Flavin) domain from AppA, a transcriptional anti-repressor from Rhodobacter sphaeroides, in Escherichia coli, photoactive holo-protein is formed through non-covalent binding of a flavin. Whereas it is generally assumed that FAD is the physiological chromophore of this photo-perception domain in vivo, E. coli can (and does) insert, depending on the growth conditions, all naturally occurring flavins, i.e. ribo flavin, FMN and FAD into this protein domain. The nature of the particular flavin bound affects the photochemical- and particularly the fluorescence properties of the N-terminal domain of this photosensory protein.