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J. Bacteriol., Dec 1995, 6751-6760, Vol 177, No. 23
J Yu, L Hederstedt and PJ Piggot
We have identified an operon in Bacillus subtilis, designated qcr, that is
thought to encode a quinone: cytochrome c reductase. Northern (RNA blot)
analysis suggests a tricistronic operon. The operon is located at about 200
degrees on the B. subtilis map. Disruption of the operon leads to loss of a
22-kDa cytochrome c from membrane preparations. The structure of the
putative protein products of the qcr operon suggests a protein complex that
is closely related to but distinct from known cytochrome bc1 and b6f
complexes, which catalyze electron transfer from a quinol to a c-type
cytochrome or to plastocyanin. QcrA is similar to Rieske-type iron-sulfur
proteins; QcrB is similar in size and sequence to b-type cytochromes from
b6f complexes; and QcrC has a novel structure that resembles a fusion of a
subunit IV (found in b6f complexes) to a cytochrome c. Transcription of the
operon is induced at the end of exponential growth from a sigma A-like
promoter. This transition state induction appears to be dependent on the
downregulation of abrB expression, which is mediated by Spo0A activation.
As bacteria move from the transition state into sporulation, transcription
of the operon is reduced in a sigma F- dependent manner.
Copyright © 1995, American Society for Microbiology
The cytochrome bc complex (menaquinone:cytochrome c reductase) in Bacillus subtilis has a nontraditional subunit organization
Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
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