Conformational changes triggered by Mg2+ mediate transactivator function

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.