HRG4 (HGMW-approved symbol UNC119) is a novel human photoreceptor-enriched gene coding for a 240-amino-acid protein. Initially, HRG4 was shown to be 57% homologous to a newly discovered Caenorhabditis elegans gene, mutated in a coordination mutant and involved in chemosensation. Recently, HRG4 has been localized to the photoreceptor synapses in the outer plexiform layer of the retina. The HRG4 gene was cloned and characterized to facilitate its analysis as a potential pathogenic gene. The gene consisted of five coding exons, spread over approximately 8 kb of genomic DNA. The transcriptional start site was 14 bp upstream of the cDNA, 68 bp upstream of the putative translational initiation codon. Five GC boxes were identified in a 100-bp upstream region, along with a photoreceptor conserved element 1-like sequence at -603. Another photoreceptor gene-associated sequence, Ret-1, was present in intron 1, 71 bp downstream of the exon 1/intron 1 border. A CpG island encompassing exon 1 and sequences just before and after it was present. The gene was fine mapped to 17q11.2, facilitating its future consideration as a candidate for retinal diseases mapped to the same region.