In Vivo Characterization of Phytochrome-Phycocyanobilin Adducts in Yeast (*)
- From the § Institut für Biologie II, Albert-Ludwigs-Universität Freiburg, Schänzlestrasse 1, 79104 Freiburg, Federal Republic of Germany
- ¶To whom correspondence should be addressed: Tel.: 49-761-2032683; Fax: 49-761-203-2629.
Abstract
The in vivo reconstitution of phycocyanobilin with apophytochrome leads to photoreversible adducts in living yeast cells. Investigations with the rice phytochrome A phycocyanobilin adduct (PHYA*) and the tobacco phytochrome B phycocyanobilin adduct (PHYB*) show that the protein stability in yeast is independent of the form of the photoreceptor.
After in vivo assembly and irradiation with red light, 25.6% of the far-red light-absorbing form of PHYB* exhibited dark reversion with a half-life time of approximately 20 min. Control experiments with PHYA* revealed no dark reversion. The data indicate that the molecular basis for this reaction is the formation of heterodimers between the red and the far-red light absorbing form of phytochrome.
Electron microscopic in situ localizations and in vitro sequestering experiments showed that phytochrome A was able to sequester in yeast. On the electron microscopic level, the sequestered areas of phytochrome from etiolated plants and yeast are indistinguishable. The sequestering reaction in yeast is independent of the formation of the far-red light absorbing form of phytochrome. Therefore, we discuss a new model for this reaction in plants.
Since it is unlikely that yeast cells contain elements that distinguish between phytochrome A and B, we conclude that sequestering and dark reversion reflect intrinsic properties of phytochrome.
Footnotes
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↵* This work was supported by the Deutsche Forschungsgemeinschaft SFB 388 and an International Human Frontier Science Organization (HSFPO) grant (to E. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 The abbreviations used are:
- Pr
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red light absorbing form of phytochrome
- Pfr
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far-red light absorbing form of phytochrome
- PHYA*
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rice phytochrome A-phycocyanobilin adduct
- PHYB*
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tobacco phytochrome B-phycocyanobilin adduct
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SAP sequestered areas of phytochrome.
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↵2T. Kunkel, G. Neuhaus, A. Batschauer, N.-H. Chua, and E. Schäfer, manuscript in preparation.
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- Received May 11, 1995.
- Revision received June 21, 1995.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
