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Multiple Phosphorylation Sites Confer Reproducibility of the Rod's Single-Photon Responses
Thuy Doan,1
Ana Mendez,4
Peter B. Detwiler,2
Jeannie Chen,4*
Fred Rieke2,3*
Abstract:
Although signals controlled by single molecules are expectedto be inherently variable, rod photoreceptors generate reproducibleresponses to single absorbed photons. We show that this unexpectedreproducibility—the consistency of amplitude and durationof rhodopsin activity—varies in a graded and systematicmanner with the number but not the identity of phosphorylationsites on rhodopsin's C terminus. These results indicate thateach phosphorylation site provides an independent step in rhodopsindeactivation and that collectively these steps tightly controlrhodopsin's active lifetime. Other G protein cascades may exploita similar mechanism to encode accurately the timing and numberof receptor activation.
1 Program in Neurobiology and Behavior, University of Washington, Seattle, WA 98195, USA. 2 Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195, USA. 3 Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195, USA. 4 Department of Ophthalmology and Cell and Neurobiology Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, USA.
* To whom correspondence should be addressed. E-mail: rieke{at}u.washington.edu (F.R.); jeannie{at}usc.edu (J.C.)
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