Unc-119 Homolog (UNC119)

HRG4 is enriched in the photoreceptors of the retina. HRG4 shares strong homology with the C. elegans unc119 protein and it can functionally complement the C. elegans unc119 mutation. It has been localized to the photoreceptor synapses in the outer plexiform layer of the retina, and suggested to play a role in the mechanism of photoreceptor neurotransmitter release through the synaptic vesicle cycle. Two transcript variants encoding different isoforms have been described for this gene.The predicted 240-amino acid human and rat proteins both contain an N-terminal region rich in proline and glycine followed by a region with a mixture of alpha helices, beta sheets, and turns. Sequence comparisons indicated that the proline-glycine domains of RRG4 and HRG4 share only 67% homology, while the rest of the sequence is 100% identical.