INTEGRATION HOST FACTOR AFFECTS THE OXYGEN-REGULATED EXPRESSION OF PHOTOSYNTHESIS GENES IN RHODOBACTER-CAPSULATUS

The puf and puc operons of Rhodabacter capsulatus, which encode pigmen t binding proteins, are regulated by oxygen tension. Strain IR4 which carries a point mutation in the himA gene for integration host factor (IHF) shows a delayed increase in the amount of photosynthetic complex es after reduction of oxygen tension when compared to the isogenic wil d-type strain. This delay in the formation of photosynthetic complexes correlates with a delay in increasing the level of transcription of t he puf and puc operons, whereas the transcription of the bchD genes is not affected by IHF. Several IHF binding sites can be identified upst ream of the puf and puc transcriptional starts by in vitro footprint a nalysis. Our results suggest that IHF facilitates the binding of other trans-acting factors, e.g. RegA, which in turn stimulate transcriptio n of the puf and puc genes under low oxygen tension.