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T Isayama, S Shulga-Morskoy, J Lem, CL Makino; Greatly Prolonged Photoresponses in Transgenic Mouse Rods Expressing Mutant S202D Transducin . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1835.
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Purpose: Transducin links photon absorption by rhodopsin to a biochemical cascade that results in an electrical response in retinal rods. RGS9 accelerates the GTPase activity of the transducin α-subunit (Gαt ) that is necessary for the termination of the photoresponse. The switch II region of Gαt plays an important role in the interaction between Gαt and RGS9, as well as with its effector, PDE. Involvement of S202 in transducin has been implicated in the acceleration of transducin's GTPase activity by RGS9 in site-specific mutagenesis experiments of chimeric Gαt /Gαi carried out in vitro (Natochin & Artemyev, 1998). We have explored the impact of the mutation of S202 in transducin on phototransduction in intact rods by recording the photoresponses of single mouse rods induced to express a mutant S202D Gαt in place of the native Gαt . Methods: Retinal morphology was examined in wild type and S202D mice by light microscopy. Single cell suction electrode recordings were performed to evaluate the photoresponses of rods from wild type and S202D mice. Results: Retinas of S202D mice at 2-3 months of age appeared to develop normally without any sign of degeneration. S202D rods proved capable of generating photoresponses with normal flash sensitivity. While the time to peak of the dim flash response was not different from wild type, the recovery of the response was greatly prolonged. As a result, the integration time was six-fold greater than normal. The rate-limiting time constant of photoresponse recovery derived from the analysis of saturating flash responses was 15-fold slower than normal in S202D rods. Conclusion: These results are in general agreement with prior recordings by Burns and Baylor of mouse rods in which the gene for RGS9-1 was knocked out (Chen et al., 2000). Thus, the S202D mutation appears to impair the interaction between transducin and RGS9 without affecting transducin activation by rhodopsin or PDE activation by transducin. M. Natochin, & N.O. Artemyev. J. Biol. Chem. 273:4300-4303, 1998. C.-K. Chen, M.E. Burns, W. He, T.G. Wensel, D.A. Baylor, & M.I. Simon. Nature 403:557-560, 2000.
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