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Conformational changes triggered by Mg2+ mediate transactivator function.

Ganduri Swapna1, Matheswaran Saravanan, Valakunja Nagaraja

  • 1Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India.

Biochemistry
|January 28, 2009
PubMed
Summary
This summary is machine-generated.

Transactivator protein C uses magnesium ions to bind DNA and activate transcription in bacteriophage mu. Specific residues coordinate Mg(2+), enabling essential allosteric transitions for phage gene expression.

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Area of Science:

  • Molecular Biology
  • Virology
  • Biochemistry

Background:

  • Transactivator protein C is crucial for bacteriophage mu's transition to late gene expression.
  • Protein C mediates a multistep activation of the mom promoter (P(mom)), involving promoter unwinding and enhanced RNA polymerase clearance.
  • High-affinity DNA binding by Protein C, dependent on Mg(2+), is essential for its transactivation function.

Purpose of the Study:

  • To identify the specific residues in transactivator protein C responsible for coordinating Mg(2+) ions.
  • To elucidate the role of Mg(2+)-induced allosteric transitions in Protein C's DNA binding and transcriptional activation.
  • To understand the mechanism by which Mg(2+) regulates transcription factor function.

Main Methods:

  • Site-directed mutagenesis was used to alter residues within the putative metal binding motif (E(26)X(10)D(37)X(2)D(40)) of Protein C.
  • Analysis of Mg(2+) ion binding capabilities of wild-type and mutant proteins.
  • Assessment of DNA binding affinity and transcriptional activation levels following mutations.

Main Results:

  • Residues E26 and D40 were identified as critical for Mg(2+) ion coordination.
  • Mutations in these residues resulted in altered Mg(2+)-induced conformations, reduced DNA binding affinity, and decreased transcription activation.
  • The study provides the first evidence for Mg(2+)-induced allosteric transitions regulating transcription factor activity.

Conclusions:

  • Specific residues (E26, D40) in bacteriophage mu Protein C are essential for Mg(2+) binding and subsequent allosteric conformational changes.
  • These Mg(2+)-dependent allosteric transitions are vital for high-affinity DNA binding and efficient transcriptional activation of the mom promoter.
  • This work highlights the significant, yet previously uncharacterized, role of metal ion-induced allostery in regulating transcription factor function.