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A Novel Form of the G Protein β Subunit Gβ5 Is Specifically Expressed in the Vertebrate Retina

Watson, A. John and Aragay, Anna M. and Slepak, Vladlen Z. and Simon, Melvin I. (1996) A Novel Form of the G Protein β Subunit Gβ5 Is Specifically Expressed in the Vertebrate Retina. Journal of Biological Chemistry, 271 (45). pp. 28154-28160. ISSN 0021-9258. doi:10.1074/jbc.271.45.28154.

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The G protein β subunit, Gβ_5, is predominantly expressed in the central nervous system. In rodent brain, Gβ_5 is expressed as a protein with an apparent molecular mass of 39,000 daltons (39 kDa). We have identified an additional Gβ_5 immunoreactive protein of apparent size 44 kDa in the vertebrate retina. Molecular cloning and sequencing of polymerase chain reaction products revealed that the cDNA encoding the larger species of Gβ_5 (Gβ_(5L)) was identical to the shorter form with the addition of 126 base pairs of 5′ DNA sequence potentially encoding an in-frame 42-amino acid extension. Sequencing of mouse Gβ_5 genomic clones demonstrated that the 126-base pair of retinal-specific coding material is derived from a hitherto undetected 5′ exon. During sucrose density gradient fractionation of bovine retinas, the 44-kDa Gβ_(5L) protein co-purified with rod outer segment membranes. Incubation of rod outer segment membranes with the nonhydrolyzable guanine nucleotide, GTPγS (guanosine 5′-3-O-(thio)triphosphate), which released the Gβ subunit of transducin (Gβ_1), failed to remove Gβ_(5L). The 39-kDa Gβ_5 protein displayed differential association with retinal and brain membranes. In the retina, Gβ_5 was present as a soluble protein and was undetectable in the membrane fraction, whereas in the brain approximately 70% of Gβ_5 was associated with cellular membranes. In transient COS-7 cell expression experiments, Gβ_(5L) formed functional Gβγ dimers and Gαβγ heterotrimers, and activated phosphoinositide-specific phospholipase Cβ_2 in a manner indistinguishable from the 39-kDa Gβ_5 protein. The cloning of the retinal-specific Gβ_(5L) cDNA suggests the existence of potentially novel G protein-mediated signaling cascades in photoreception.

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Additional Information:© 1996 American Society for Biochemistry and Molecular Biology, Inc. Received for publication, June 7, 1996, and in revised form, August 16, 1996. This work was supported by Grant GM34236 from the National Institutes of Health (to M. I. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. We thank our colleagues in the Simon laboratory for materials and N. Gautam, D. Oprian, and P. Casey for helpful discussions. Automated DNA sequencing was performed by S. Marsh, R. Colayco, and B. Perry. The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) U69145[GenBank].
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Issue or Number:45
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ID Code:29209
Deposited On:08 Feb 2012 23:39
Last Modified:09 Nov 2021 17:04

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