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J. Bacteriol., Jan 1997, 41-45, Vol 179, No. 1
I Korsa and A Bock
The FhlA protein belongs to the NtrC family of transcriptional regulators.
It induces transcription from the -12/-24 promoters of the genes of the
formate regulon by sigma54 RNA polymerase. FhlA is activated by binding of
the ligand formate and does not require phosphorylation. A mutational
analysis of the fhLA gene portion coding for the A and C domains was
conducted with the aim of gaining information on the interaction between
formate binding and ATP hydrolysis plus transcription activation. Four
mutations were identified, all located in the A domain; one of them
rendered transcription completely independent from the presence of formate,
and the others conferred a semiconstitutive phenotype. The FhlA protein of
one of the semiconstitutive variants was purified. Catalytic efficiency of
ATP hydrolysis of the mutant FhlA was increased in the absence of formate
in the same manner as formate influences the activity of wild- type FhlA.
Moreover, in vitro transcription occurred at much lower threshold
concentrations of the mutant protein and of nucleoside triphosphates than
with the wild-type FhlA.
Copyright © 1997, American Society for Microbiology
Characterization of fhlA mutations resulting in ligand-independent transcriptional activation and ATP hydrolysis
Lehrstuhl fur Mikrobiologie der Universitat Munchen, Munich, Germany.
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