title: Conformational changes triggered by Mg2+ mediate transactivator function.
abstract: 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 Mg(2+)-dependent fashion. Mg(2+)-mediated conformational transition in C is necessary for its DNA binding and transactivation. We have determined the residues in C which coordinate Mg(2+), to induce allosteric transition in the protein, required for the specific interaction with DNA. Residues E26 and D40 in the putative metal binding motif (E(26)X(10)D(37)X(2)D(40)) present toward the N-terminus of the protein are found to be important for Mg(2+) ion binding. Mutations in these residues lead to altered Mg(2+)-induced conformation, compromised DNA binding, and reduced levels of transcription activation. Although Mg(2+) 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.
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Ganduri
authors.initials: G
authors.lastname: Swapna
authors.forename: Matheswaran
authors.initials: M
authors.lastname: Saravanan
authors.forename: Valakunja
authors.initials: V
authors.lastname: Nagaraja
mesh_terms: D000595:Amino Acid Sequence; D010583:Bacteriophage mu / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000737:chemistry* / Q000378:metabolism*; D004247:DNA / Q000235:genetics / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry*; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D015534:Trans-Activators / Q000737:chemistry* / Q000378:metabolism*; D015533:Transcriptional Activation; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; C090591:C protein, Bacteriophage Mu; D015534:Trans-Activators; D014764:Viral Proteins; D004247:DNA; D008274:Magnesium