Diacylglycerol kinase that converts diacylglycerol/DAG into phosphatidic acid/phosphatidate/PA and regulates the respective levels of these two bioactive lipids (PubMed:15024004). 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:15024004). 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). Has a decreased affinity for ATP and a reduced diacylglycerol kinase activity. Has no preference for any of the diacylglycerols in terms of the acyl chain composition. Has no diacylglycerol kinase activity. 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(+) 1,2-di-(9Z-octadecenoyl)-sn-glycerol + ATP = 1,2-di-(9Z-octadecenoyl)-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(+) 1-octadecanoyl-2-(9Z,12Z)-octadecadienoyl-sn-glycerol + ATP = 1-octadecanoyl-2-(9Z,12Z-octadecadienoyl)-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-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycerol + ATP = 1-octadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-phosphate + ADP + H(+) Activated by phosphatidylserine. 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 (PubMed:21119615). Interacts (via PDZ-binding motif) with DLG2 (PubMed:21119615). Interacts (via PDZ-binding motif) with DLG3 (PubMed:21119615). May interact with RASGRP3; involved in the regulation of RASGRP3 activity (By similarity). Excluded from inhibitory synapses (PubMed:21119615). Localization between cytoplasm and nucleus is regulated by protein kinase C (By similarity). Both in the detergent soluble and particulate fractions (PubMed:15024004). Not detected in detergent soluble fraction. Not detected in detergent soluble fraction. Specifically expressed in brain (at protein level) (PubMed:15024004, PubMed:21119615). Expressed in hippocampus, cerebellum, brain stem and spinal cord (at protein level) (PubMed:21119615). Highly expressed in hippocampus, cerebellar cortex, olfactory bulb, and olfactory tubercle and to lower extent in the cerebral cortex, caudate putamen, and thalamus. Not detected in the white matter (PubMed:15024004). Also expressed in eye (PubMed:15024004). Major isoform in brain (at protein level). Minor isoform in brain (at protein level). Expressed in brain (at protein level). Expression gradually increases in the first weeks after birth (at protein level). Belongs to the eukaryotic diacylglycerol kinase family.