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General Comment |
Using a subtractive hybridization strategy, Higashide et al. (1996) identified a retina-specific cDNA that they designated
HRG4 (human retinal gene-4). Northern blot analysis revealed that the approximately 1.4-kb HRG4 mRNA is expressed
specifically in human retina. The authors also cloned a cDNA encoding RRG4, the rat HRG4 homolog. 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.
Mutations in the C. elegans unc119 gene lead to defects in locomotion, feeding behavior, and chemosensation. Higashide et al. (1996) observed that HRG4 shares strong homology with the C. elegans unc119 protein.
NCBI Summary:
This gene is specifically expressed in the photoreceptors in the retina. The encoded product 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.
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