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Journal of Bacteriology, March 1999, p. 1755-1766, Vol. 181, No. 6
Department of Molecular Biology, The Hebrew
University-Hadassah Medical School, Jerusalem 91120, Israel
Received 20 October 1998/Accepted 8 January 1999
The Escherichia coli transcriptional antiterminator
protein BglG inhibits transcription termination of the bgl
operon in response to the presence of
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Characterization of the Dimerization Domain in
BglG, an RNA-Binding Transcriptional Antiterminator from
Escherichia coli
-glucosides in the growth
medium. BglG is an RNA-binding protein that recognizes a specific
sequence partially overlapping the two terminators within the
bgl transcript. The activity of BglG is determined by its
dimeric state which is modulated by reversible phosphorylation. Thus,
only the nonphosphorylated dimer binds to the RNA target site and
allows readthrough of transcription. Genetic systems which test
dimerization and antitermination in vivo were used to map and delimit
the region which mediates BglG dimerization. We show that the last 104 residues of BglG are required for dimerization. Any attempt to shorten
this region from the ends or to introduce internal deletions abolished
the dimerization capacity of this region. A putative leucine zipper
motif is located at the N terminus of this region. The role of the
canonical leucines in dimerization was demonstrated by their
substitution. Our results also suggest that the carboxy-terminal 70 residues, which follow the leucine zipper, contain another dimerization
domain which does not resemble any known dimerization motif. Each of
these two regions is necessary but not sufficient for dimerization. The
BglG phosphorylation site, His208, resides at the junction
of the two putative dimerization domains. Possible mechanisms by which
the phosphorylation of BglG controls its dimerization and thus its
activity are discussed.
*
Corresponding author. Mailing address: Department of
Molecular Biology, The Hebrew University-Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel. Phone: 972 2 675 8460. Fax: 972 2 6784010. E-mail: amster{at}cc.huji.ac.il.
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