Diacylglycerol kinase that converts diacylglycerol/DAG into phosphatidic acid/phosphatidate/PA and regulates the respective levels of these two bioactive lipids. 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. 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 (By similarity). By controlling the diacylglycerol/DAG-mediated activation of RASGRP3, negatively regulates the Rap1 signaling pathway (PubMed:15894621). May play a role in presynaptic diacylglycerol/DAG signaling and control neurotransmitter release during metabotropic glutamate receptor-dependent long-term depression (PubMed:21119615). 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 (By similarity). 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 (PubMed:21119615). May interact with RASGRP3; involved in the regulation of RASGRP3 activity (Probable). Excluded from inhibitory synapses (By similarity). Localization between cytoplasm and nucleus is regulated by protein kinase C (By similarity). Both in the detergent soluble and particulate fractions (By similarity). In brain, expressed in the hippocampus and cerebellum with stronger expression in the Purkinje cell layer (at protein level) (PubMed:21119615). Expressed in kidney (PubMed:15894621). Homozygous knockout mice lacking Dgki do not display overt phenotype (PubMed:15894621). They are slower to habituation to a novel environment, but have normal levels of locomotor activity, anxiety, and motor coordination (PubMed:21119615). They display a small increase in presynaptic release probability and synapses show a reduction in metabotropic glutamate receptor-dependent long-term depression (PubMed:21119615). Belongs to the eukaryotic diacylglycerol kinase family.