Ong O C, Hu K, Rong H, Lee R H, Fung B K
Jules Stein Eye Institute, Department of Molecular and Medical Pharmacology, University of California at Los Angeles School of Medicine 90095, USA.
Genomics. 1997 Aug 15;44(1):101-9. doi: 10.1006/geno.1997.4814.
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 gamma subunit (G gamma c, previously named G gamma b), which may play a key role in coupling the cone visual pigment to phosphodiesterase (O. C. Ong et al., 1995, J. Biol. Chem. 270:8495-8500). We report here the characterization of human G gamma c and its gene structure. Human G gamma c subunit shares a high degree of sequence identity with the corresponding bovine G gamma c isoform (85%) and human rod G gamma 1 (63%). The protein is specifically localized in cones, as indicated by immunohistochemical staining using anti-G gamma c antibodies. Nucleotide sequence analysis of the G gamma c gene (GNGT2) reveals a structure consisting of three exons and two introns, with the intron splice sites similar to that of the rod G gamma 1 gene (GNGT1). By using fluorescence in situ hybridization, we have further localized the human GNGT2 gene to chromosome 17q21. The elucidation of the G gamma c gene structure would facilitate the identification of genetic defects associated with cone degeneration.
脊椎动物视杆和视锥光感受器中的光转导由结构同源但又不同的信号蛋白组调节。我们之前在牛视网膜中鉴定出一种视锥特异性G蛋白γ亚基（Gγc，之前称为Gγb），它可能在将视锥视觉色素与磷酸二酯酶偶联中起关键作用（O.C. Ong等人，1995年，《生物化学杂志》270:8495 - 8500）。我们在此报告人Gγc的特性及其基因结构。人Gγc亚基与相应的牛Gγc同工型具有高度的序列同一性（85%），与人视杆Gγ1具有63%的序列同一性。使用抗Gγc抗体进行免疫组织化学染色表明，该蛋白特异性定位于视锥中。对Gγc基因（GNGT2）的核苷酸序列分析揭示了一个由三个外显子和两个内含子组成的结构，其内含子剪接位点与视杆Gγ1基因（GNGT1）的相似。通过荧光原位杂交，我们进一步将人GNGT2基因定位到17号染色体q21区。Gγc基因结构的阐明将有助于鉴定与视锥退化相关的遗传缺陷。
