Master regulator of synaptic plasticity that self-assembles into virion-like capsids that encapsulate RNAs and mediate intercellular RNA transfer from motorneurons to muscles (PubMed:29328915). Arc1 protein is released from motorneurons in extracellular vesicles that mediate the transfer of Arc1 mRNA into muscle cells, where Arc1 mRNA can undergo activity-dependent translation (PubMed:29328915). Intercellular transfer od Arc1 mRNA is required for synaptic plasticity at the neuromuscular junction (PubMed:29328915). May play a role in energy balance: required for regulation of body fat by a specific population of brain neurons, named E347, that are necessary and sufficient for proper body fat storage (PubMed:26209258). Homooligomer; homooligomerizes into virion-like capsids. Forms virion-like extracellular vesicles that are released from neurons (PubMed:29328915). Present at pre- and postsynaptic sites of the neuromuscular junction (PubMed:29328915). Expressed in a specific population of brain neurons, named E347, that are necessary and sufficient for proper body fat storage. Up-regulated following stimulation of E347 brain neurons. The protein is evolutionarily related to retrotransposon Gag proteins (PubMed:29328915, PubMed:29328916). 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 (PubMed:29328915, PubMed:29328916). Tetrapod and fly Arc protein-coding genes originated independently from distinct lineages of Ty3/gypsy retrotransposons (PubMed:29328916). Strong reduction in the number of synaptic boutons at neuromuscular junction in third-instar larvae. Belongs to the ARC/ARG3.1 family.