Molecular Cloning and Characterization of the G Protein γ Subunit of Cone Photoreceptors

• Published in: The Journal of biological chemistry 1995-04, Vol.270 (15), p.8495-8500
• Main Authors: Ong, Olivia C., Yamane, Harvey K., Phan, Kim B., Fong, Henry K.W., Bok, Dean, Lee, Rehwa H., Fung, Bernard K.-K.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Cattle; Cloning, Molecular; DNA, Complementary; GTP-Binding Proteins - genetics; GTP-Binding Proteins - immunology; GTP-Binding Proteins - metabolism; Immune Sera; Immunohistochemistry; Molecular Sequence Data; Protein Prenylation; Retinal Cone Photoreceptor Cells - metabolism; RNA, Messenger - metabolism; Sequence Homology, Amino Acid
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.15.8495

The phototransduction process in cones has been proposed to involve a G protein that couples the signal from light-activated visual pigment to the effector cyclic GMP phosphodiesterase. Previously, we have identified and purified a Gβγ complex composed of a Gβ3isoform and an immunochemically distinct Gγ subunit (Gγ8) from bovine retinal cones (Fung, B. K.-K., Lieberman, B. S., and Lee, R. H. (1992) J. Biol. Chem. 267, 24782-24788; Lee, R. H., Lieberman, B. S., Yamane, H. K., Bok, D., and Fung, B. K.-K. (1992a) J. Biol. Chem. 267, 24776-24781). Based on the partial amino acid sequence of this cone Gγ8, we screened a bovine retinal cDNA library and isolated a cDNA clone encoding Gγ8. The cDNA insert of this clone includes an open reading frame of 207 bases encoding a 69-amino acid protein. The predicted protein sequence of Gγ8shares a high degree of sequence identity (68%) with the Gγ (Gγ1) subunit of rod transducin. Similar to rod Gγ1, it terminates in a CIIS motif that is the site for post-translational modification by farnesylation. Messenger RNA for Gγ8is present at a high level in the retina and at a very low level in the lung, but is undetectable in other tissues. Immunostaining of bovine retinal sections with an antipeptide antibody against the N-terminal region of Gγ8further shows a differential localization of Gγ8to cones with a pattern indistinguishable from that of Gβ3. This finding suggests that Gβ3γ8is a component of cone transducin involved in cone phototransduction and color vision.