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J. Bacteriol., 06 1995, 2990-2997, Vol 177, No. 11
SN Ponnampalam, JJ Buggy and CE Bauer
For most species of purple photosynthetic bacteria, the presence of
molecular oxygen represses synthesis of carotenoids and
bacteriochlorophyll. In this study we characterize a strain of Rhodobacter
capsulatus, DB469, which contains a genomic disruption of an open reading
frame in the photosynthesis gene cluster termed ORF469. Characterization of
the steady-state level of bacteriochlorophyll synthesis demonstrates that
disruption of ORF469 results in a 2.5-fold increase in aerobic synthesis of
bacteriochlorophyll over that observed with the parent strain. Utilizing
reporter plasmids that contain transcriptional fusions of lacZ to various
carotenoid and bacteriochlorophyll biosynthesis genes, we also demonstrate
that disruption of ORF469 leads to an approximate twofold increase in
bacteriochlorophyll and carotenoid gene expression under anaerobic growth
conditions. Similar analysis with reporter plasmids that contain
translational fusions of lacZ to the puf, puh, and puc operons demonstrates
that disruption of ORF469 leads to elevated levels of aerobic transcription
of light harvesting-II genes (puc), without affecting light harvesting-I or
reaction center gene expression (puf and puh, respectively). Gel mobility
analysis demonstrates that DB469 cells lack a DNA-binding protein that
interacts with a palindromic sequence in the bchC promoter region. The
results of this study indicate that ORF469 codes for a DNA-binding protein
that acts as an aerobic repressor of promoters for bacteriochlorophyll,
carotenoid, and light harvesting-II gene expression.
Copyright © 1995, American Society for Microbiology
Characterization of an aerobic repressor that coordinately regulates bacteriochlorophyll, carotenoid, and light harvesting-II expression in Rhodobacter capsulatus
Department of Chemistry, Indiana University, Bloomington 47405, USA.
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