We are also introducing a new promoter and gene pair to iGEM that forms a copper-dependent repressible system. Since the library of metal sensitive promoters was relatively small on the Registry of Standard Biological Parts, we decided to investigate a metal-dependent system. We chose mmoR and a σ54 promoter associated with it from a bacterium called Methylosinus trichosporium OB3b. mmoR is a σ54-dependent transcriptional activator.