Dopamine receptor responsible for neuronal signaling in the mesolimbic system of the brain, an area of the brain that regulates emotion and complex behavior. Activated by dopamine, but also by epinephrine and norepinephrine, and by numerous synthetic agonists and drugs (PubMed:9003072, PubMed:16423344, PubMed:27659709, PubMed:29051383). Agonist binding triggers signaling via G proteins that inhibit adenylyl cyclase (PubMed:7512953, PubMed:7643093, PubMed:16423344, PubMed:27659709, PubMed:29051383). Modulates the circadian rhythm of contrast sensitivity by regulating the rhythmic expression of NPAS2 in the retinal ganglion cells (By similarity). Signaling in response to agonists such as dopamine, epinephrine and norepinephrine is modulated by Na(+); lower Na(+) levels result in higher receptor activity (in vitro). Forms homo- and heterooligomers with DRD2. D4.7 allele exhibits higher affinity for homodimers compared to DRD2 heterodimers, while alleles D42. and 4.4 have similar affinities for both. The interaction with DRD2 may modulate agonist-induced downstream signaling (PubMed:21184734). Interacts with CLIC6 (By similarity). Interacts with GPRASP1 (PubMed:12142540). May interact with ADORA2A (PubMed:20836733). Interacts with KLHL12 (PubMed:18303015). Highly expressed in retina. Detected at much lower levels in brain, in amygdala, thalamus, hypothalamus, cerebellum and pituitary. Polyubiquitinated by the BCR(KLHL12) E3 ubiquitin ligase complex: polyubiquitination does not lead to degradation of DRD4 protein. Palmitoylated. Palmitoylation of the C-terminal Cys is important for normal expression at the cell membrane. The number of repeats of 16 amino acids in the third cytoplasmic loop is highly polymorphic and varies among different alleles. Alleles corresponding in size to a 2 (D4.2), 3 (D4.3), 4 (D4.4), 5 (D4.5), 6 (D4.6), 7 (D4.7) and 9 (D4.9) repeats have been described. The sequence shown is that of allele D4.4. The polymorphic repeat sequence has little influence on DRD4-binding profiles and might not be essential for G protein interaction. Belongs to the G-protein coupled receptor 1 family.