A synthetic peptide includes an amino acid sequence that: has 70-75%, 75-80%, 80-85%, 85-90%, 90-95% or 95-100% homology with an RpoN box of Region III of an RpoN protein and binds specifically to a −24, −12, or −24/−12 site(s) of an RpoN promoter. The synthetic peptide is effective for repressing transcription and/or gene expression from a binding site of interest, and the binding site of interest is an RpoN binding site or a cryptic promoter upstream of an RpoN binding site.
