Dual use of the transcriptional repressor (CtBP2)/ribbon synapse (RIBEYE) gene: how prevalent are multifunctional genes?

Vertebrates have ribbon synapses in the retina and in other sensory structu res that are specialized for rapid, tonic release of synaptic vesicles'. Th e lamellar sheets of the ribbon situated at right angles to the plasma memb rane are lined with synaptic vesicles that undergo exocytosis under the inf luence of Ca2+. Synaptic ribbons act as a conveyer belt to accelerate the r elease of this ready supply of synaptic vesicles at the presynaptic membran es. Although the protein composition of the terminals of ribbon synapses is generally similar to that of ordinary synapses in nervous tissue, much les s is known about the composition of the ribbons themselves. RIM, a universa l component of presynaptic active zones that interacts with rab3 on the syn aptic vesicle, has been localized to the ribbons(2). In addition, the kines in motor protein, KIF3A, is associated with the ribbons and other organelle s in presynaptic nerve terminals(3). Recently, a similar to 120 kDa protein called RIBEYE has been identified in purified ribbons of bovine retina. Th e RIBEYE cDNA was cloned and its gene identified in the database.