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J. Bacteriol., Aug 1995, 4609-4618, Vol 177, No. 16
M Gomelsky and S Kaplan
A new gene, the product of which is involved in the regulation of
photosynthesis gene expression in the anoxygenic photosynthetic bacterium
Rhodobacter sphaeroides 2.4.1, has been identified. The isolation of this
gene, designated appA (activation of photopigment and puc expression), was
based on its ability, when provided in extra copies, to partially suppress
mutations in the two-component PrrB-PrrA regulatory system. The presence of
extra copies of the appA gene in either prrB, prrA, or wild-type strains
resulted in an activation of puc::lacZ expression under aerobic conditions.
Constructed AppA null mutants did not grow photosynthetically and were
impaired in the synthesis of both bacteriochlorophyll and carotenoids, as
well as the structural proteins of the photosynthetic spectral complexes.
When grown anaerobically in the dark, these mutants accumulated
bacteriochlorophyll precursors. The expression of lacZ fusions to several
photosynthesis genes and operons, including puc, puf, and bchF, was
decreased in the AppA mutant strains in comparison with the wild type. To
examine the role of AppA involvement in bacteriochlorophyll biosynthesis,
we inactivated an early gene, bchE, of the bacteriochlorophyll pathway in
both wild-type and AppA- mutant backgrounds. The double mutant, AppA-
BchE-, was found to be severely impaired in photosynthesis gene expression,
similar to the AppA- BchE+ mutant and in contrast to the AppA+ BchE-
mutant. This result indicated that AppA is more likely involved in the
regulation of expression of the bch genes than in the biosynthetic pathway
per se. The appA gene was sequenced and appears to encode a protein of 450
amino acids with no obvious homology to known proteins.
Copyright © 1995, American Society for Microbiology
appA, a novel gene encoding a trans-acting factor involved in the regulation of photosynthesis gene expression in Rhodobacter sphaeroides 2.4.1
Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston 77030, USA.
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