Interacting selectively and non-covalently with a specific DNA sequence and interacting selectively and non-covalently with any metal ion(s) and responding, e.g. by conformational change, to changes in the cellular level of those metal ions, in such a way that metal ion binding regulates the activity of the transcription factor in order to activate or increase the frequency, rate or extent of cellular DNA-dependent transcription by an RNA polymerase. Specific mechanisms include increasing or decreasing the ability of the transcription factor to interact selectively and non-covalently with a specific DNA sequence (for example S. cerevisiae Cup2p or the prokaryotic SmtB/ArsR family, changing the conformation of transcription factor bound DNA between the apo- and metal-bound forms of the transcription factor. Additional mechanisms may exist.