Trans-acting factor that binds specifically to the consensus nucleotide sequence 5'-TNCGTACAA-3' of AP1 promoter. Promotes both vegetative phase change and flowering. Binds 2 Zn(2+) ions per subunit. Mostly located in nucleus. Expressed in the rib meristem and inter-primordial tissue of the inflorescence apex. Increases during floral transition and stay high thereafter. Negatively regulated by microRNAs miR156 and miR157. The SBP-type zinc finger is required for the binding to DNA.