Transcriptional activation by the PHD finger is inhibited through an adjacent leucine zipper that binds 14-3-3 proteins

The PHD finger, a Cys(4)-His-Cys(3) zinc finger, is found in many regulator y proteins from plants or animals which are frequently associated with chro matin-mediated transcriptional regulation. We show here that the PHD finger activates transcription in yeast, plant and animal cells, In plant homeodo main transcription factors the PHD finger is combined with an upstream leuc ine zipper. Both domains together form a highly conserved 180 amino acid re gion called the ZIP/PHDf motif and transcriptional activity of the PHD fing er Is masked when embedded in this motif, Our results indicate that the ZIP /PHDf domain is a potential regulatory domain of PHDf-HD proteins. The leuc ine zipper upstream of the PHD finger interacts with 14-3-3GF14 mu from Ara bidopsis thaliana and 14-3-3GF14-12 from maize via a leucine zipper conserv ed in helix 4 of various 14-3-3 proteins from plants and animals. PHD-type plant homeodomain proteins consequently may represent potential targets of 14-3-3 signalling.