THE PLANT CELL, Vol 1, Issue 6 591-597, Copyright © 1989 by American Society of Plant Biologists
Deletion Mutagenesis of the Cytochrome b559 Protein Inactivates the Reaction Center of Photosystem II
H. B. Pakrasi, B. A. Diner, JGK. Williams and C. J. Arntzen
Central Research and Development Department, E.I. du Pont de Nemours and Company, Wilmington, Delaware 19898
In green plant-like photosynthesis, oxygen evolution is catalyzed by a
thylakoid membrane-bound protein complex, photosystem II. Cytochrome b559,
a protein component of the reaction center of this complex, is absent in a
genetically engineered mutant of the cyanobacterium, Synechocystis 6803
[Pakrasi, H.B., Williams, J.G.K., and Arntzen, C.J. (1988). EMBO J. 7,
325-332]. In this mutant, the genes psbE and psbF, encoding cytochrome
b559, were deleted by targeted mutagenesis. Two other protein components,
D1 and D2 of the photosystem II reaction center, are also absent in this
mutant. However, two chlorophyll-binding proteins, CP47 and CP43, as well
as a manganese-stabilizing extrinsic protein component of photosystem II
are stably assembled in the thylakoids of this mutant. Thus, this deletion
mutation destabilizes the reaction center of photosystem II only. The
mutant also lacks a fluorescence maximum peak at 695 nm (at 77 K) even
though the CP47 protein, considered to be the origin of this fluorescence
peak, is present in this mutant. We propose that the fluorescence at 695 nm
originates from an interaction between the reaction center of photosystem
II and CP47. The deletion mutant shows the absence of variable fluorescence
at room temperature, indicating that its photosystem II complex is
photochemically inactive. Also, photoreduction of QA, the primary acceptor
quinone in photosystem II, could not be detected in the mutant. We conclude
that cytochrome b559 plays at least an essential structural role in the
reaction center of photosystem II.
