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J. Bacteriol., 08 1995, 4442-4450, Vol 177, No. 15
B Kusian, R Bednarski, M Husemann and B Bowien
Autotrophic CO2 fixation via the Calvin carbon reduction cycle in
Alcaligenes eutrophus H16 is genetically determined by two highly
homologous cbb operons, one of which is located on the chromosome and the
other on megaplasmid pHG1 of the organism. An activator gene, cbbR, lies in
divergent orientation only 167 bp upstream of the chromosomal operon and
controls the expression of both cbb operons. The two 5'- terminal genes of
the operons, cbbLS, coding for ribulose-1,5- bisphosphate
carboxylase/oxygenase, were sequenced. Mapping of the 5' termini of the
2.1-kb cbbLS transcripts by primer extension and by nuclease S1 treatment
revealed a single transcriptional start point at the same relative position
for the chromosomal and plasmid-borne cbb operons. The derived cbb operon
promoter showed similarity to sigma 70- dependent promoters of Escherichia
coli. For the 1.4-kb transcripts of cbbR, the transcriptional start points
were different in autotrophic and heterotrophic cells. The two
corresponding cbbR promoters overlapped the cbb operon promoter and also
displayed similarities to sigma 70-dependent promoters. The deficient cbbR
gene located on pHG1 was transcribed as well. A newly constructed double
operon fusion vector was used to determine the activities of the cbb
promoters. Fusions with fragments carrying the cbb intergenic control
regions demonstrated that the cbb operon promoters were strongly regulated
in response to autotrophic versus heterotrophic growth conditions. In
contrast, the cbbR promoters displayed low constitutive
activities.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Characterization of the duplicate ribulose-1,5-bisphosphate carboxylase genes and cbb promoters of Alcaligenes eutrophus
Institut fur Mikrobiologie, Georg-August-Universitat Gottingen, Germany.
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