Conformational Changes Triggered by Mg2+ Mediate Transactivator Function

Transactivator protein C of bacteriophage mu is essential for the transition from middle to late gene expression during the phage life cycle. The unusual, multistep activation of mom promoter (P mom ) by C protein involves activator-mediated promoter unwinding to recruit RNA polymerase and subsequen...

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Bibliographic Details
Published in:Biochemistry (Easton) 2009-03, Vol.48 (11), p.2347-2354
Main Authors: Swapna, Ganduri, Saravanan, Matheswaran, Nagaraja, Valakunja
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Bacteriophage mu - chemistry
Bacteriophage mu - genetics
Bacteriophage mu - metabolism
Basic Helix-Loop-Helix Leucine Zipper Transcription Factors - chemistry
Basic Helix-Loop-Helix Leucine Zipper Transcription Factors - metabolism
DNA - genetics
DNA - metabolism
Magnesium - chemistry
Molecular Sequence Data
Protein Binding
Protein Conformation
Trans-Activators - chemistry
Trans-Activators - metabolism
Transcriptional Activation
Viral Proteins - chemistry
Viral Proteins - metabolism
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Summary:Transactivator protein C of bacteriophage mu is essential for the transition from middle to late gene expression during the phage life cycle. The unusual, multistep activation of mom promoter (P mom ) by C protein involves activator-mediated promoter unwinding to recruit RNA polymerase and subsequent enhanced promoter clearance of the enzyme. To achieve this, C binds its site overlapping the −35 region of the mom promoter with a very high affinity, in Mg2+-dependent fashion. Mg2+-mediated conformational transition in C is necessary for its DNA binding and transactivation. We have determined the residues in C which coordinate Mg2+, to induce allosteric transition in the protein, required for the specific interaction with DNA. Residues E26 and D40 in the putative metal binding motif (E26X10D37X2D40) present toward the N-terminus of the protein are found to be important for Mg2+ ion binding. Mutations in these residues lead to altered Mg2+-induced conformation, compromised DNA binding, and reduced levels of transcription activation. Although Mg2+ is widely used in various DNA transaction reactions, this report provides the first insights on the importance of the metal ion-induced allosteric transitions in regulating transcription factor function.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi8022448