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Journal of Bacteriology, August 1998, p. 4080-4088, Vol. 180, No. 16
Department of Applied Biological Sciences,
School of Agricultural Sciences, Nagoya University, Nagoya 464-01, Japan
Received 20 April 1998/Accepted 4 June 1998
There are three binding sites for NtcA (nirI,
nirII, and nirIII), the global nitrogen
regulator of cyanobacteria, in the DNA region between the two
divergently transcribed operons (nirA and nirB operons) involved in nitrate assimilation in
Synechococcus sp. strain PCC 7942. Using the
luxAB reporter system, we showed that nirI and
nirIII, which are located 23 bp upstream from the
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
cis-Acting Sequences Required for NtcB-Dependent,
Nitrite-Responsive Positive Regulation of the Nitrate Assimilation
Operon in the Cyanobacterium Synechococcus sp. Strain
PCC 7942
10
promoter element of nirA and nirB,
respectively, are required for induction by nitrogen depletion of the
nirA and nirB operons, respectively.
The induction of nirA operon transcription was a prerequisite for the nitrite-responsive positive regulation of the
transcription by NtcB, a LysR-type protein. The NtcA-binding site
nirII, located in the middle of the nirA-nirB
intergenic region, and a potential binding site for a LysR-type protein
(TGCAN5TGCA; designated L1), located between
nirI and nirII, were required for the
nitrite-responsive, NtcB-dependent enhancement of nirA operon transcription. Although the requirement for the L1 site was consistent with the involvement of the LysR family protein NtcB in
transcriptional regulation, NtcB did not bind to the nirA regulatory region in vitro in the presence of nitrite and NtcA, suggesting the involvement of some additional factor(s) in the regulation. An L1-like inverted repeat with the consensus sequence TGCN7GCA was conserved in the nirA promoter
region of cyanobacteria, being centered at position
23 with respect
to the NtcA-binding site corresponding to nirI, which
suggested the common occurrence of nitrite-responsive regulation of the
nitrate assimilation operon among cyanobacteria.
*
Corresponding author. Mailing address: Department of
Applied Biological Sciences, School of Agricultural Sciences, Nagoya University, Nagoya 464-01 Japan. Phone: 81-52-789-4106. Fax:
81-52-789-4104. E-mail:
g44512a{at}nucc.cc.nagoya-u.ac.jp.
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