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J. Biol. Chem., Vol. 279, Issue 47, 49010-49018, November 19, 2004

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Conserved Transcriptional Activators of the Xenopus Rhodopsin Gene^*

S. Leigh Whitaker and Barry E. Knox

From the Departments of Biochemistry & Molecular Biology and Ophthalmology, SUNY Upstate Medical University, Syracuse, New York 13210

Vertebrate rhodopsin promoters exhibit striking sequence identities proximal to the initiation site, suggesting that conserved transcription factors regulate rhodopsin expression in these animals. We identify and characterize two transcriptional activators of the Xenopus rhodopsin gene: homologs of the mammalian Crx and Nrl transcription factors, XOtx5 and XL-Nrl (originally named XL-maf), respectively. XOtx5 stimulated transcription 10-fold in human 293 cells co-transfected with a plasmid containing the rhodopsin promoter (–508 to +41) upstream of luciferase, similar to the 6-fold stimulation with human Crx. XL-Nrl stimulated transcription 27-fold in mammalian 293 cells co-transfected with the rhodopsin luciferase reporter, slightly more than the 17-fold stimulation with Nrl. Together, the Xenopus transcription factors synergistically activated the rhodopsin promoter (140-fold), as well as in combination with mammalian homologs. Deletion of the Nrl-response element, TGCTGA, eliminated the synergistic activation by both mammalian and Xenopus transcription factors. Deletion of the conserved ATTA sequences (Ret-1 or BAT-1), binding sites for Crx, did not significantly decrease activation by Crx/XOtx5. However, there was increased activation by Nrl/XL-Nrl and an increased synergy when the Ret-1 site was disrupted. These results illustrate conservation of mechanisms of retinal gene expression among vertebrates. In transgenic tadpoles, XOtx5 and XL-Nrl directed premature and ectopic expression from the Xenopus rhodopsin promoter-GFP transgene. Furthermore, activation of the endogenous rhodopsin gene was also observed in some animals, showing that XOtx5 and XL-Nrl can activate the promoter in native chromatin environment.

Received for publication, June 1, 2004 , and in revised form, July 27, 2004.

^* This work was supported by National Institutes of Health Grants EY-11256 and EY-12975 (to B. E. K.), an unrestricted grant to the Research to Prevent Blindness to SUNY Upstate Medical University Department of Ophthalmology, and the Lions of Central New York. 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.

The on-line version of this article (available at http://www.jbc.org) contains Supplemental Figs. S1–S4.

To whom correspondence should be addressed: Dept. of Biochemistry & Molecular Biology, SUNY Upstate Medical University, 750 E. Adams St. Syracuse, NY 13210. Tel.: 315-464-8719; Fax: 315-464-8750; E-mail: knoxb{at}upstate.edu.

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