Master regulator of synaptic plasticity that self-assembles into virion-like capsids that encapsulate RNAs and mediate intercellular RNA transfer in the nervous system. ARC protein is released from neurons in extracellular vesicles that mediate the transfer of ARC mRNA into new target cells, where ARC mRNA can undergo activity-dependent translation. ARC capsids are endocytosed and are able to transfer ARC mRNA into the cytoplasm of neurons. Acts as a key regulator of synaptic plasticity: required for protein synthesis-dependent forms of long-term potentiation (LTP) and depression (LTD) and for the formation of long-term memory. Regulates synaptic plasticity by promoting endocytosis of AMPA receptors (AMPARs) in response to synaptic activity: this endocytic pathway maintains levels of surface AMPARs in response to chronic changes in neuronal activity through synaptic scaling, thereby contributing to neuronal homeostasis. Acts as a postsynaptic mediator of activity-dependent synapse elimination in the developing cerebellum by mediating elimination of surplus climbing fiber synapses. Accumulates at weaker synapses, probably to prevent their undesired enhancement. This suggests that ARC-containing virion-like capsids may be required to eliminate synaptic material. Homooligomer; homooligomerizes into virion-like capsids. Forms virion-like extracellular vesicles that are released from neurons. Enriched in postsynaptic density of dendritic spines. Accumulates at weaker synapses may be required to prevent their undesired enhancement. Associated with the cell cortex of neuronal soma and dendrites. Expressed at various levels throughout the brain. By synaptic activity. Transcript level significantly increased in auditory cortex as well as two higher-associative brain regions by auditory imprinting stimulus in newborn chicks. The protein is evolutionarily related to retrotransposon Gag proteins: it contains large N- and C-terminal domains that form a bi-lobar architecture similar to the capsid domain of human immunodeficiency virus (HIV) gag protein. It contains structural elements found within viral Gag polyproteins originated from the Ty3/gypsy retrotransposon family and retains the ability to form virion-like capsid structures that can mediate mRNA transfer between cells. Tetrapod and fly Arc protein-coding genes originated independently from distinct lineages of Ty3/gypsy retrotransposons. Palmitoylation anchors the protein into the membrane by allowing direct insertion into the hydrophobic core of the lipid bilayer. Belongs to the ARC/ARG3.1 family.