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J. Biol. Chem., Vol. 281, Issue 45, 34421-34429, November 10, 2006

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Functional and Biochemical Analysis of the N-terminal Domain of Phytochrome A^*

Julieta L. Mateos¹, Juan Pablo Luppi, Ouliana B. Ogorodnikova^¶, Vitaly A. Sineshchekov^¶, Marcelo J. Yanovsky, Silvia E. Braslavsky, Wolfgang Gärtner, and Jorge J. Casal²

From the Max-Planck-Institut für Bioanorganische Chemie, Postfach 101356, D-45413 Mülheim an der Ruhr, Germany, IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, Avenue San Martín 4453,1417 Buenos Aires, Argentina, and ^¶Biology Department, M. V. Lomonosov Moscow State University, Moscow 119992, Russia

Phytochrome A (phyA) is a versatile plant photoreceptor that mediates responses to brief light exposures (very low fluence responses, VLFR) as well as to prolonged irradiation (high irradiance responses, HIR). We identified the phyA-303 mutant allele of Arabidopsis thaliana bearing an R384K substitution in the GAF subdomain of the N-terminal half of phyA. phyA-303 showed reduced phyA spectral activity, almost normal VLFR, and severely impaired HIR. Recombinant N-terminal half oat of PHYA bearing the phyA-303 mutation showed poor incorporation of chromophore in vitro, despite the predicted relatively long distance (>13 Å) between the mutation and the closest ring of the chromophore. Fusion proteins bearing the N-terminal domain of oat phyA, -glucuronidase, green fluorescent protein, and a nuclear localization signal showed physiological activity in darkness and mediated VLFR but not HIR. At equal protein levels, the phyA-303 mutation caused slightly less activity than the fusions containing the wild-type sequence. Taken together, these studies highlight the role of the N-terminal domain of phyA in signaling and of distant residues of the GAF subdomain in the regulation of phytochrome bilin-lyase activity.

Received for publication, April 12, 2006 , and in revised form, September 8, 2006.

^* This work was supported in part by Deutsche Forschungs Gemeinschaft (DFG) Grant BR 901/14-1,/14-2 (to S. E. B.), Russian Foundation for Basic Research Grant 05-04-49549 (to V. A. S.), and University of Buenos Aires (G021) and Agencia Nacional de Promoción Científica y Tecnológica (PICT 11631) grants (to J. J. C.). 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 Table S1.

¹ Supported by fellowships from National Research Council of Argentina and DFG.

² To whom correspondence should be addressed. Tel.: 5411-4524-8070; Fax: 5411-4514-8730; E-mail: casal{at}ifeva.edu.ar.

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