DNA-bend modulation in a repressor-to-activator switching mechanism.

Abstract	Recent discoveries of activator proteins that distort DNA but bear no obvious activation domains have focused attention on the role of DNA structure in transcriptional regulation. Here we describe how the transcription factor MerR can mediate repression as well as activation through stereospecific modulation of DNA structure. The repressor form of MerR binds between the -10 and -35 promoter elements of the bacterial mercury-detoxification genes, PT, allowing RNA polymerase to form an inactive complex with PT and MerR at this stress-inducible promoter. Upon mercuric ion binding, Hg-MerR converts this polymerase complex into the transcriptionally active or 'open' form. We show here that MerR bends DNA towards itself in a manner similar to the bacterial catabolite-activator protein CAP, namely at two loci demarked by DNase I sensitivity, and that the activator conformation, Hg-MeR, relaxes these bends. This activator-induced unbending, when coupled with the previously described untwisting of the operator, remodels the promoter and makes it a better template for the poised polymerase.
Authors	A Z Ansari, J E Bradner, T V O'Halloran
Journal	Nature (Nature) Vol. 374 Issue 6520 Pg. 371-5 (Mar 23 1995) ISSN: 0028-0836 [Print] England
PMID	7885478 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)
Chemical References	Bacterial Proteins Cyclic AMP Receptor Protein DNA-Binding Proteins MerR protein, Bacteria Repressor Proteins DNA DNA-Directed RNA Polymerases Deoxyribonuclease I
Topics	Bacterial Proteins (metabolism) Base Sequence Cyclic AMP Receptor Protein (metabolism) DNA (metabolism) DNA-Binding Proteins (metabolism) DNA-Directed RNA Polymerases (metabolism) Deoxyribonuclease I Gene Expression Regulation Molecular Sequence Data Nucleic Acid Conformation Operator Regions, Genetic Promoter Regions, Genetic Repressor Proteins (metabolism)

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