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 inflorescence apical meristem and young flowers. Increases during floral transition and stay high thereafter. Negatively regulated by microRNAs miR156. The SBP-type zinc finger is required for the binding to DNA.