RNA polymerase, PurR and MetR interactions at the glyA promoter of Escherichia coli

In Escherichia coli, the MetR and PurR proteins positively and negatively regulate glyA gene expression, respectively. A DNase I footprint analysis showed that both proteins bind independently to the glyA control region. The PurR protein blocks RNA polymerase (RNAP) from binding to the glyA promoter. The presence of hypoxanthine, the co-repressor of PurR, increases the ability of PurR to prevent RNAP binding, providing a model for repression of the glyA gene by PurR. In contrast, MetR alters the RNAP footprint pattern of the glyA control region. In addition, the MetR footprint is increased in the presence of RNAP, suggesting that the two proteins might interact.