MetR-mediated repression of the glyA gene in Escherichia coli

Inactivation of either of the two MetR binding sites centered at bp -143 and 121 relative to the +1 transcription start site results in reduced glyA-lacZ expression in a wild-type strain below the level seen in a metR mutant. This reduced expression is dependent on the side of the DNA helix MetR binds relative to the RNA polymerase binding site. Thus, a single MetR dimer bound to the DNA may play a physiological role in maintaining appropriate glyA gene expression, functioning as a repressor under low MetR conditions.