CLONING, CHROMOSOMAL LOCALIZATION AND FUNCTIONAL EXPRESSION OF THE GENE ENCODING THE ALPHA-SUBUNIT OF THE CGMP-GATED CHANNEL IN HUMAN CONE PHOTORECEPTORS

Cyclic nucleotide-gated (CNG) ion channels serve as final targets of s ignal transduction in vertebrate photoreceptors. While the basic mecha nisms of phototransduction are similar in rod and cone photoreceptors, both cell types express distinct sets of components of the transducti on pathway. We report here the cloning of the cDNA encoding the alpha- subunit of the cGMP-gated channel of human cone photoreceptors. The op en reading frame predicts a polypeptide of 694 amino acid residues wit h conserved functional parts and amino acid positions typical for the alpha-subunit of CNG-channels, Heterologous expression of the cDNA in Xenopus oocytes gave rise to cGMP-gated channel activity, Antiserum di rected against the C-terminus of the bovine cone CNG channel alpha-sub unit crossreacted specifically with the heterologously expressed polyp eptide and stained cone photoreceptors and weakly also the outer plexi form layer in human retinal sections. Northern blot analysis detected a prominent mRNA species of similar to 3.8 kb in human retina. The ent ire gene spans similar to 30 kb of genomic sequence and is located an the pericentric band q11.2 of human chromosome 2. The gene is composed of seven exons, with introns located at positions which are preserved with respect to the human rod gene, indicating a common ancestral gen e structure. RT-PCR analysis gave no evidence for alternatively splice d transcripts.