CHARACTERIZATION OF AN AEROBIC REPRESSOR THAT COORDINATELY REGULATES BACTERIOCHLOROPHYLL, CAROTENOID, AND LIGHT HARVESTING-II EXPRESSION INRHODOBACTER-CAPSULATUS
Sn. Ponnampalam et al., CHARACTERIZATION OF AN AEROBIC REPRESSOR THAT COORDINATELY REGULATES BACTERIOCHLOROPHYLL, CAROTENOID, AND LIGHT HARVESTING-II EXPRESSION INRHODOBACTER-CAPSULATUS, Journal of bacteriology, 177(11), 1995, pp. 2990-2997
For most species of purple photosynthetic bacteria, the presence of mo
lecular oxygen represses synthesis of carotenoids and bacteriochloroph
yll. In this study we characterize a strain of Rhodobacter capsulatus,
DB469, which contains a genomic disruption of an open reading frame i
n the photosynthesis gene cluster termed ORF469. Characterization of t
he steady-state level of bacteriochlorophyll synthesis demonstrates th
at disruption of ORF469 results in a 2.5-fold increase in aerobic synt
hesis 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 expressio
n under anaerobic growth conditions. Similar analysis with reporter pl
asmids 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), wi
thout affecting light harvesting-I or reaction center gene expression
(puf and puh, respectively). Gel mobility analysis demonstrates that D
B469 cells lack a DNA-binding protein that interacts with a palindromi
c sequence in the bchC promoter region. The results of this study indi
cate that ORF469 codes for a DNA-binding protein that acts as an aerob
ic repressor of promoters for bacteriochlorophyll, carotenoid, and lig
ht harvesting-ii gene expression.