Protein synthesizing units in presynaptic and postsynaptic domains of squid neurons

Putative protein synthesizing domains, called plaques, are characterized in the squid giant synapse and axon and in terminals of squid photoreceptor n eurons. Plaques are oval-shaped formations of about 1 mu m in size, which ( 1) generate signals that have spectroscopic electron energy loss characteri stics of ribosomes, (2) exhibit ribonuclease-sensitive binding of YOYO-1, a fluorescent RNA/DNA dye, and (3) in part hybridize with a poly(dT) oligonu cleotide. In the giant synapse plaques are abundant in the postsynaptic are a, but are absent in the presynaptic terminal. In the cortical layer of the optic lobes, plaques are localized in the large carrot-shaped presynaptic terminals of photoreceptor neurons, where they are surrounded by synaptic v esicles and mitochondria. documented that the protein synthetic activity of squid optic lobe synaptos omes is largely due to the presynaptic terminals of the photoreceptor neuro ns. The identification of ribosomes and poly(A(+))-mRNA in the plaques indi cates that these structures are sites of local protein synthesis in synapti c domains.