PLANT PHYSIOLOGY , Vol 106, Issue 4 1435-1442, Copyright © 1994 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Deletion of the Structural Gene for the NADH-Dehydrogenase Subunit 4 of Synechocystis 6803 Alters Respiratory Properties
V. A. Dzelzkalns, C. Obinger, G. Regelsberger, H. Niederhauser, M. Kamensek, G. A. Peschek and L. Bogorad
Department of Biology, Case Western Reserve University, Cleveland, Ohio 44106 (V.A.D.)
Chloroplasts and cyanobacteria contain genes encoding polypeptides
homologous to some subunits of the mitochondrial respiratory NADH-ubiquinol
oxidoreductase complex (NADH dehydrogenase). Nothing is known of the role
of the NADH dehydrogenase complex in photosynthesis, respiration, or other
functions in chloroplasts, and little is known about the specific roles of
the perhaps 42 subunits of this complex in the mitochondrion. Inactivation
of a gene for subunit 4 (ndhD-2, ndh4) of this complex in the
cyanobacterium Synechocystis 6803 has no effect on photosynthesis, judging
from the rate of photoautotrophic growth of mutant cells, but the mutant's
respiratory rate is about 6 times greater than that of wild-type cells.
Respiratory electron transport activity in cyanobacteria is associated both
with photosynthetic thylakoid membranes and with the outer cytoplasmic
membrane of the cell. Cytoplasmic membranes of mutant cells have much
greater NADH-dependent cytochrome reductase activity than preparations from
wild-type cells; this activity remains at wild-type levels in isolated
thylakoid membranes. It is suggested that the 56.6-kD product of ndhD-2 is
not essential for the activity of a cytoplasmic membrane-bound NADH
dehydrogenase but that it regulates the rate of electron flow through the
complex, establishing a link between this ndh gene and respiration. The
activity of the molecularly distinct thylakoid-bound NADH dehydrogenase is
apparently unaffected by the loss of ndhD-2.
