Zinc ions inhibit the protein-DNA complex formation between cyano-bacterial transcription factor SmtB and its recognition DNA sequences

Abstract

SmtB is a trans-acting dimeric repressor of the metal-regulated smtA gene, and the release of SmtB from the smtA operator/promoter region is essential for the tolerance to Zn2+ stress by SmtA expression. Gel retardation assaying demonstrated that different sizes of SmtB-DNA complexes were formed depending on the DNA sequences, and the amounts of these complexes decreased in the presence of Zn2+. Here, we present the first direct evidence that Zn2+ (>4 μM) inhibits the SmtB-DNA complex formation in vitro, which ensures the physiological functions of SmtB as a Zn2+ sensor and a transcription factor.