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Journal of Bacteriology, September 2000, p. 5188-5195, Vol. 182, No. 18
Department of Molecular and Cell Biology,
University of California, Berkeley, California
94720-32041; Department of
Chemistry, University of California, Davis, California
956162; and Department of
Plant and Microbial Biology, University of California, Berkeley,
California 94720-31023
Received 28 December 1999/Accepted 19 June 2000
The bacterial enhancer-binding protein NtrC is a well-studied
response regulator in a two-component regulatory system. The amino (N)-terminal receiver domain of NtrC modulates the function of
its adjacent output domain, which activates transcription by the
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Phosphorylation-Induced Signal Propagation in the Response
Regulator NtrC


54 holoenzyme. When a specific aspartate residue in the
receiver domain of NtrC is phosphorylated, the dimeric
protein forms an oligomer that is capable of ATP hydrolysis and
transcriptional activation. A chemical protein cleavage method was used
to investigate signal propagation from the
phosphorylated receiver domain of NtrC, which acts
positively, to its central output domain. The iron chelate reagent
Fe-BABE was conjugated onto unique cysteines introduced into the
N-terminal domain of NtrC, and the conjugated proteins were subjected
to Fe-dependent cleavage with or without prior
phosphorylation. Phosphorylation-dependent cleavage,
which requires proximity and an appropriate orientation of the
peptide backbone to the tethered Fe-EDTA, was particularly prominent
with conjugated NtrCD86C, in which the unique
cysteine lies near the top of
-helix 4. Cleavage occurred outside
the receiver domain itself and on the partner subunit
of the derivatized monomer in an NtrC dimer. The results are
commensurate with the hypothesis that
-helix 4 of the
phosphorylated receiver domain of NtrC interacts with
the beginning of the central domain for signal propagation. They imply that the phosphorylation-dependent interdomain and
intermolecular interactions between the receiver domain of one subunit
and the output domain of its partner subunit in an NtrC dimer
precede
and may give rise to
the oligomerization needed for
transcriptional activation.
*
Corresponding author. Mailing address: Department of
Plant and Microbial Biology, 111 Koshland Hall, no. 3102, University of
California Berkeley, Berkeley, CA 94720-3102. Phone: (510) 643-9308. Fax: (510) 642-4995. E-mail: kustu{at}nature.berkeley.edu.
Present address: CATCH Inc., Seattle, WA 98134.
Present address: School of Agricultural Biotechnology, Seoul
National University, Suweon 441-744, Korea.
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