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J. Bacteriol., 12 1996, 7080-7089, Vol 178, No. 24
G Zeng, S Ye and TJ Larson
The nucleotide sequence of the glpEGR operon of Escherichia coli was
determined. The translational reading frame at the beginning, middle, and
end of each gene was verified. The glpE gene encodes an acidic, cytoplasmic
protein of 108 amino acids with a molecular weight of 12,082. The glpG gene
encodes a basic, cytoplasmic membrane-associated protein of 276 amino acids
with a molecular weight of 31,278. The functions of GlpE and GlpG are
unknown. The glpR gene encodes the repressor for the glycerol 3-phosphate
regulon, a protein predicted to contain 252 amino acids with a calculated
molecular weight of 28,048. The amino acid sequence of the glp repressor
was similar to several repressors of carbohydrate catabolic systems,
including those of the glucitol (GutR), fucose (FucR), and
deoxyribonucleoside (DeoR) systems of E. coli, as well as those of the
lactose (LacR) and inositol (IolR) systems of gram-positive bacteria and
agrocinopine (AccR) system of Agrobacterium tumefaciens. These repressors
constitute a family of related proteins, all of which contain approximately
250 amino acids, possess a helix-turn-helix DNA-binding motif near the
amino terminus, and bind a sugar phosphate molecule as the inducing signal.
The DNA recognition helix of the glp repressor and the nucleotide sequence
of the glp operator were very similar to those of the deo system. The
presumptive recognition helix of the glp repressor was changed by site-
directed mutagenesis to match that of the deo repressor or, in a separate
construct, to abolish DNA binding. Neither altered form of the glp
repressor recognized the glp or deo operator, either in vivo or in vitro.
However, both altered forms of the glp repressor were negatively dominant
to the wild-type glp repressor, indicating that the inability to bind DNA
with high affinity was due to alteration of the DNA-binding domain, not to
an inability to oligomerize or instability of the altered repressors. For
the first time, analysis of repressors with altered DNA-binding domains has
verified the assignment of the helix- turn-helix motif of the
transcriptional regulators in the deoR family.
Copyright © 1996, American Society for Microbiology
Repressor for the sn-glycerol 3-phosphate regulon of Escherichia coli K- 12: primary structure and identification of the DNA-binding domain
Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg 24061-0308, USA.
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