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Journal of Bacteriology, July 2001, p. 4183-4189, Vol. 183, No. 14
Department of Microbiology and Immunology,
Emory University School of Medicine, Atlanta, Georgia 30322
Received 29 January 2001/Accepted 20 April 2001
Proteins that have a structure similar to those of LuxR and FixJ
comprise a large subfamily of transcriptional activator proteins. Most
members of the LuxR-FixJ family contain a similar amino-terminal receiver domain linked by a small region to a carboxy-terminal domain
that contains an amino acid sequence similar to the helix-turn-helix (HTH) motif found in other DNA-binding proteins. GerE from
Bacillus subtilis is the smallest member of the
LuxR-FixJ family. Its 74-amino-acid sequence is similar over its entire
length to the DNA binding region of this protein family, including the
HTH motif. Therefore, GerE provides a simple model for studies of the
role of this HTH domain in DNA binding. Toward this aim, we sought to
identify the amino acids within this motif that are important for the
specificity of binding to DNA. We examined the effects of single base
pair substitutions in the high-affinity GerE binding site on the
sigK promoter and found that nucleotides at positions
+2, +3, and +4 relative to the transcription start site on the
sigK promoter are important for a high-affinity
interaction with GerE. We next examined the effects of single alanine
substitutions at two positions in the HTH region of GerE on binding to
wild-type or mutant target sites. We found that the substitution of an
alanine for the threonine at position 42 of GerE produced a protein
that binds with equal affinity to two sites that differ by 1 bp,
whereas wild-type GerE binds with different affinities to these two
sites. These results provide evidence that the amino acyl residues in
or near the putative HTH region of GerE and potentially other members
of the LuxR-FixJ family determine the specificity of DNA binding.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.14.4183-4189.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Identification of a DNA Binding Region in GerE from
Bacillus subtilis
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Emory University School of Medicine,
Atlanta, GA 30322. Phone: (404) 727-5969. Fax: (404) 727-3659. E-mail: moran{at}microbio.emory.edu.
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