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J. Bacteriol., 01 1997, 128-134, Vol 179, No. 1
M Gomelsky and S Kaplan
The AppA protein plays an essential regulatory role in development of the
photosynthetic apparatus in the anoxygenic phototrophic bacterium
Rhodobacter sphaeroides 2.4.1 (M. Gomelsky and S. Kaplan, J. Bacteriol.
177:4609-4618, 1995). To gain additional insight into both the role and
site of action of AppA in the regulatory network governing photosynthesis
gene expression, we investigated the relationships between AppA and other
known regulators of photosynthesis gene expression. We determined that AppA
is dispensable for development of the photosynthetic apparatus in a ppsR
null background, where PpsR is an aerobic repressor of genes involved in
photopigment biosynthesis and puc operon expression. Moreover, all
suppressors of an appA null mutation thus far isolated, showing improved
photosynthetic growth, were found to contain mutations in the ppsR gene.
Because ppsR gene expression in R. sphaeroides 2.4.1 appears to be largely
independent of growth conditions, we suggest that regulation of repressor
activity occurs predominately at the protein level. We have also found that
PpsR functions as a repressor not only under aerobic but under anaerobic
photosynthetic conditions and thereby is involved in regulating the
abundance of the light harvesting complex II, depending on light intensity.
It seems likely therefore, that PpsR responds to an integral signal (e.g.,
changes in redox potential) produced either by changes in oxygen tension or
light intensity. The profile of the isolated suppressor mutations in PpsR
is in accord with this proposition. We propose that AppA may be involved in
a redox-dependent modulation of PpsR repressor activity.
Copyright © 1997, American Society for Microbiology
Molecular genetic analysis suggesting interactions between AppA and PpsR in regulation of photosynthesis gene expression in Rhodobacter sphaeroides 2.4.1
Department of Microbiology and Molecular Genetics, the University of Texas Medical School at Houston, 77030, USA.
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