Diacylglycerol kinase that converts diacylglycerol/DAG into phosphatidic acid/phosphatidate/PA and regulates the respective levels of these two bioactive lipids (PubMed:9830018, PubMed:23949095). Thereby, acts as a central switch between the signaling pathways activated by these second messengers with different cellular targets and opposite effects in numerous biological processes (Probable). Has probably no preference for any of the diacylglycerols in terms of the acyl chain composition, especially for the acyl chain at the sn-2 position (PubMed:9830018). By controlling the diacylglycerol/DAG-mediated activation of RASGRP3, negatively regulates the Rap1 signaling pathway. May play a role in presynaptic diacylglycerol/DAG signaling and control neurotransmitter release during metabotropic glutamate receptor-dependent long-term depression (By similarity). a 1,2-diacyl-sn-glycerol + ATP = a 1,2-diacyl-sn-glycero-3-phosphate + ADP + H(+) 1,2-di-(9Z-octadecenoyl)-sn-glycerol + ATP = 1,2-di-(9Z-octadecenoyl)-sn-glycero-3-phosphate + ADP + H(+) 1-octadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycerol + ATP = 1-octadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-phosphate + ADP + H(+) 1-octadecanoyl-2-(9Z,12Z)-octadecadienoyl-sn-glycerol + ATP = 1-octadecanoyl-2-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phosphate + ADP + H(+) Lipid metabolism; glycerolipid metabolism. Interacts (via PDZ-binding motif) with DLG4; controls the localization of DGKI to the synapse (PubMed:21119615). Interacts (via PDZ-binding motif) with DLG1 (By similarity). Interacts (via PDZ-binding motif) with DLG2 (By similarity). Interacts (via PDZ-binding motif) with DLG3 (By similarity). May interact with RASGRP3; involved in the regulation of RASGRP3 activity (By similarity). Excluded from inhibitory synapses (By similarity). Localization between cytoplasm and nucleus is regulated by protein kinase C (PubMed:9830018). Both in the detergent soluble and particulate fractions (By similarity). Specifically expressed in brain and retina (PubMed:9830018). In brain, highly expressed in hippocampus, caudate nucleus, occipital pole, cerebral cortex, and cerebellum (PubMed:9830018). Also detected in kidney (PubMed:15894621). Belongs to the eukaryotic diacylglycerol kinase family.