Postsynaptic scaffolding protein that plays a critical role in synaptogenesis and synaptic plasticity by providing a platform for the postsynaptic clustering of crucial synaptic proteins. High levels in postsynaptic density of neuronal cells. At 3 days-post-fertilization (dpf), expressed strongly in neurons in the ventral hindbrain and tegmentum and diffusely in the dorsal hindbrain and optic tectum. Also expressed in the diencephalon and the prospective olfactory bulb. Expression in non-spiny type-XIV tectal neurons is mostly diffuse. Over the next 7 days, as the dendritic arbor develops, expression becomes progressively more punctate, becoming localized to sites of synapse formation. At 4 dpf, expressed in the inner and outer plexiform layers of the retina and in the optic chiasm. L27 domain is required for targeting to postsynaptic density. Ubiquitinated by MDM2 in response to NMDA receptor activation, leading to proteasome-mediated degradation of DLG4 which is required for AMPA receptor endocytosis. Palmitoylated. Palmitoylation is required for targeting to postsynaptic density, plasma membrane and synapses. Belongs to the MAGUK family.