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Molecular and Cellular Biology, February 2000, p. 1116-1123, Vol. 20, No. 4
Department of Plant Sciences, Weizmann
Institute of Science, Rehovot 76100, Israel
Received 7 September 1999/Returned for modification 20 October
1999/Accepted 10 November 1999
Light has been proposed to stimulate the translation of
Chlamydomonas reinhardtii chloroplast psbA mRNA
by activating a protein complex associated with the 5' untranslated
region of this mRNA. The protein complex contains a redox-active
regulatory site responsive to thioredoxin. We identified RB60, a
protein disulfide isomerase-like member of the protein
complex, as carrying the redox-active regulatory site composed of
vicinal dithiol. We assayed in parallel the redox state of RB60 and
translation of psbA mRNA in intact chloroplasts. Light
activated the specific oxidation of RB60, on the one hand, and reduced
RB60, probably via the ferredoxin-thioredoxin system, on the other.
Higher light intensities increased the pool of reduced RB60 and the
rate of psbA mRNA translation, suggesting that a counterbalanced action of reducing and oxidizing activities modulates the translation of psbA mRNA in parallel with fluctuating
light intensities. In the dark, chemical reduction of the vicinal
dithiol site did not activate translation. These results suggest a
mechanism by which light primes redox-regulated translation by an
unknown mechanism and then the rate of translation is determined by the reduction-oxidation of a sensor protein located in a complex bound to
the 5' untranslated region of the chloroplast mRNA.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Translation of Chloroplast psbA mRNA Is
Modulated in the Light by Counteracting Oxidizing and Reducing
Activities
*
Corresponding author. Mailing address: Department
of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel. Phone: 972-8-934-2382. Fax: 972-8-934-4181. E-mail:
Avihai.Danon{at}weizmann.ac.il.
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