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

Aseem Z. Ansari, James E. Bradner, Thomas V. O’halloran*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

174 Scopus citations


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 regulation1. Here we describe how the transcription factor MerR can mediate repression as well as activation through stereospecific modulation of DNA structure. The represser 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 promoter2, 3. Upon mercuric ion binding, Hg−MerR converts this polymerase complex into the transcriptionally active or 'open' form2−4. 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−MerR, relaxes these bends. This activator-induced unbending, when coupled with the previously described untwisting of the operator5, remodels the promoter and makes it a better template for the poised polymerase.

Original languageEnglish (US)
Pages (from-to)370-375
Number of pages6
Issue number6520
StatePublished - Mar 23 1995

ASJC Scopus subject areas

  • General


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