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J. Bacteriol., 05 1995, 2335-2342, Vol 177, No. 9
CD Archer and T Elliott
The 14 nuo genes encode the subunits of the type I (energy-conserving) NADH
dehydrogenase, a key component of the respiratory chain. Salmonella
typhimurium, like Escherichia coli, has two enzymes that can oxidize NADH
and transfer electrons to ubiquinone, but only the type I enzyme
translocates protons across the membrane to generate a proton motive force.
Cells with the type I enzyme are energetically more efficient; the role of
the type II enzyme (encoded by ndh) is not established, but it may function
like a relief valve to allow more rapid NADH recycling. Here, we have
investigated transcription of the nuo gene cluster, primarily in S.
typhimurium. Studies with polar insertion mutants demonstrate that these
genes are arranged as a single, large operon that is expressed from a
complex promoter region upstream of nuoA. The DNA sequence of the promoter
region was determined, and primer extension analysis of nuo transcripts was
used to map four major RNA 5' ends to this region. A set of lac operon
fusions to various DNA segments from the nuo promoter region was also
constructed. Analysis of these fusions confirmed the presence of at least
two nuo promoters. Mutations in the global regulatory genes arcA, oxrA
(fnr), crp, cya, and katF were tested for effects on expression of the nuo
operon. However, none of the mutations tested had a large effect on
expression of type I NADH dehydrogenase.
Copyright © 1995, American Society for Microbiology
Transcriptional control of the nuo operon which encodes the energy- conserving NADH dehydrogenase of Salmonella typhimurium
Department of Microbiology, University of Alabama at Birmingham 35294, USA.
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