A putative transcription factor binding to the upstream region of the puf operon in Rhodobacter sphaeroides

Gel shift assays of the upstream region of the puf operon in Rhodobacter sphaeroides were performed using cell-free extracts from cells grown under various culture conditions. The results suggested that a protein binding to the upstream region functioned as a repressor-like substance of the expression of the operon by oxygen tension or light. The density of the shifted band of cell-free extracts from cells irradiated with blue light under semi-aerobic conditions was higher than that with red light. Phosphatase treatment of the cell-free extracts strongly increased the DNA-binding affinity of the protein.