Diacylglycerol kinase (DGK) and protein kinase C (PKC) are two different enzyme families that interact with diacylglycerol. Both enzymes contain cysteine-rich C1 domains with a zinc finger-like structure. Most of the C1 domains of PKCs show strong phorbol-12,13-dibutyrate (PDBu) binding with nanomolar dissociation constants (K-d'S). However, there has been no experimental evidence that phorbol esters bind to the C1 domains of DGKs. We focused on DGK gamma because its C1A domain has a high degree of sequence homology to those of PKCs, and because DGK gamma translocates from the cytoplasm to the plasma membrane following 12-O-tetradecanoylphorbol-13-acetate treatment similar to PKCs. Two C1 domains of DGKy (DGK gamma -C1A and DGK gamma -C1B) were synthesized and tested for their PDBu binding along with whole DGK gamma (Flag-DGK gamma) expressed in COS-7 cells. DGK gamma -C1A and Flag-DGK gamma showed strong PDBu binding affinity, while DGK gamma -C1B was completely inactive. Scatchard analysis of DGK gamma -C1A and Flag-DGK gamma gave K-d'S of 3.1 and 4.4 nM, respectively, indicating that the major PDBu binding site of DGKy is C1A. This is the first evidence that DGK gamma is a specific receptor of tumor-promoting phorbol esters.