CpG island in the region of an autosomal dominant polycystic kidney disease locus defines the 5′ end of a gene encoding a putative proton channel

In an attempt to isolate candidate genes for autosomal dominant polycystic kidney disease, a number of CpG-rich islands have been identified from a region defined genetically as the site of disease mutations. Genomic fragments adjacent to one of these islands were used to isolate cDNAs from both HeLa cells and cultured cystic epithelium that encode a 155-amino acid peptide having four putative transmembrane domains. The corresponding transcript was found in all tissues tested but was most abundant in brain and kidney. Potential control response elements were identified in the genomic region 5′ to the initiation codon. The deduced amino acid sequence has 93% similarity to the 16-kDa proteolipid component that is believed to be part of the proton channel of the vacuolar H⁺-ATPase. Possible roles for a mutated proton channel in the pathogenesis of cystic disease were considered. However, sequencing of cDNAs corresponding to both alleles of an affected individual revealed no differences in the deduced amino acid sequence. Moreover, transcript size and abundance were not altered in cystic kidney.