Transcription factor that participates in reprogramming global gene expression during copper deficiency in order to improve the metal uptake and prioritize its distribution to copper proteins of major importance (Probable). Binds directly to 5'-GTAC-3' motifs in the microRNA (miRNA) promoter of the stress-responsive miRNAs miR398b and miR398c to activate their transcription. During copper deficiency, activates the copper transporters COPT1 and COPT2, and the copper chaperone CCH, directly or indirectly via miRNAs. Required for the expression of the miRNAs miR397, miR408 and miR857 (PubMed:19122104). Acts coordinately with HY5 to regulate miR408 and its target genes in response to changes in light and copper conditions (PubMed:25516599). Activates miR857 and its target genes in response to low copper conditions (PubMed:26511915). Involved in cadmium stress response by regulating miR397a, miR398b, miR398c and miR857 (PubMed:27352843). Required for iron homeostasis during copper deficiency (PubMed:22374396). Binds 2 Zn(2+) ions per subunit. Homodimer (PubMed:25207797). Interacts with KIN17 (PubMed:24335506). Interacts with HY5 (PubMed:25516599). Nuclear localization with a speckled distribution pattern. Expressed in roots rosette leaves, cauline leaves, stems, flowers and siliques. Expressed constitutively during plant development. The SBP-type zinc finger is required for the binding to DNA. Retarded growth and hypersensitivity to copper deprivation. May be due to a competing donor splice site. Truncated N-terminus.