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J. Bacteriol., 06 1997, 3534-3540, Vol 179, No. 11
TB Bartnikas, IE Tosques, WP Laratta, J Shi and JP Shapleigh
A gene cluster which includes genes required for the expression of nitric
oxide reductase in Rhodobacter sphaeroides 2.4.3 has been isolated and
characterized. Sequence analysis indicates that the two proximal genes in
the cluster are the Nor structural genes. These two genes and four distal
genes apparently constitute an operon. Mutational analysis indicates that
the two structural genes, norC and norB, and the genes immediately
downstream, norQ and norD, are required for expression of an active Nor
complex. The remaining two genes, nnrT and nnrU, are required for
expression of both Nir and Nor. The products of norCBQD have significant
identity with products from other denitrifiers, whereas the predicted nnrT
and nnrU gene products have no similarity with products corresponding to
other sequences in the database. Mutational analysis and functional
complementation studies indicate that the nnrT and nnrU genes can be
expressed from an internal promoter. Deletion analysis of the regulatory
region upstream of norC indicated that a sequence motif which has identity
to a motif in the gene encoding nitrite reductase in strain 2.4.3 is
critical for nor operon expression. Regulatory studies demonstrated that
the first four genes, norCBQD, are expressed only when the oxygen
concentration is low and nitrate is present but that the two distal genes,
nnrTU, are expressed constitutively.
Copyright © 1997, American Society for Microbiology
Characterization of the nitric oxide reductase-encoding region in Rhodobacter sphaeroides 2.4.3
Department of Microbiology, Cornell University, Ithaca, New York 14853- 8101, USA.
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