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Protein Science, Vol 5, Issue 6 1195-1197, Copyright © 1996 by Cold Spring Harbor Laboratory Press
FOR THE RECORD |
M. R. GRYK, O. JARDETZKY, L. S. KLIG and C. YANOFSKY
Stanford Magnetic Resonance Laboratory, Stanford University, Stanford, California 94305-5055
Trp repressor (25 kDa) is a regulatory protein that controls transcription initiation in the tryptophan biosynthetic operon and at least four other operons in Escherichia coli. An alanine to valine mutation (AV77) in the DNA binding domain is known to increase repressor activity at the trp operator in vivo, but not in vitro. We report here the amide proton exchange rates for the DNA-binding domains of both the wild-type and AV77 proteins. We find that the alanine to valine change stabilizes the flexible DNA-binding domain of the repressor. We present in vivo data showing that, although the AV77 repressor is more inhibitory at the trp operator than the wild-type repressor, it does not have increased activity at the aroH or trpR operator; repression at the aroH operator is, in fact, reduced. Our results suggest that the flexibility exhibited by the wild-type repressor allows a broader range of repressor/DNA interactions, whereas the increased rigidity resulting from the AV77 change limits the repressor's effectiveness at some operators.
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