Gene Structure and Chromosome Localization of the GγcSubunit of Human Cone G-Protein (GNGT2)

Phototransduction in the vertebrate rod and cone photoreceptors is regulated by structurally homologous and yet distinct groups of signaling proteins. We have previously identified in bovine retinas a cone-specific G-protein γ subunit (Gγc, previously named Gγ8), which may play a key role in coupling the cone visual pigment to phosphodiesterase (O. C. Onget al.,1995,J. Biol. Chem.270: 8495–8500). We report here the characterization of human Gγcand its gene structure. Human Gγcsubunit shares a high degree of sequence identity with the corresponding bovine Gγcisoform (85%) and human rod Gγ1(63%). The protein is specifically localized in cones, as indicated by immunohistochemical staining using anti-Gγcantibodies. Nucleotide sequence analysis of the Gγcgene (GNGT2) reveals a structure consisting of three exons and two introns, with the intron splice sites similar to that of the rod Gγ1gene (GNGT1). By using fluorescencein situhybridization, we have further localized the human GNGT2 gene to chromosome 17q21. The elucidation of the Gγcgene structure would facilitate the identification of genetic defects associated with cone degeneration.