Control of photosystem genes in Rhodobacter capsulatus

Two environmental factors, oxygen and high light intensity, are known to repress synthesis of the Rhodobacter capsulatus photosystem. One level of regulation is the control of light harvesting and reaction centre gene expression at the point of transcription initiation. This has recently been shown to involve transcriptional activators which exhibit sequence similarity to members of the 'two-component' class of prokaryotic regulators. An additional level of regulation involves the formation of 'superoperons' that transcriptionally link pigment biosynthesis operons with operons that code for the light harvesting and reaction centre structural genes. A final level of regulation involves the selective degradation of reaction centre mRNA transcripts which influence the stoichiometric synthesis of the light harvesting and reaction centre complexes.