In vivo and in vitro footprinting of a light-regulated promoter in the cyanobacterium Fremyella diplosiphon.

Certain filamentous cyanobacteria, such as Fremyella diplosiphon, modulate the components of their light-harvesting complexes, the phycobilisomes, and undergo complex morphological changes in response to the wavelength of incident light, or light quality. The operon encoding the subunits of phycoerythrin, cpeBA, is transcriptionally activated in green light and is expressed at very low levels in red light. To begin elucidating the signal transduction pathway between the detection of specific light wavelengths and changes in gene expression, we have used in vivo footprinting to show that a protein is bound to the region upstream of the cpeBA transcription start site in both red and green light: two guanosine residues at -55 and -65 bp are protected from dimethyl sulfate modification in vivo.