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Identification of the Domains for DNA Binding and Transactivation Function of C Protein from Bacteriophage Mu

Paul, Bindu D and Kanhere, Aditi and Chakraborty, Atanu and Bansal, Manju and Nagaraja, Valakunja (2003) Identification of the Domains for DNA Binding and Transactivation Function of C Protein from Bacteriophage Mu. In: Proteins: Structure, Function, and Genetics, 52 (2). pp. 272-282.


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The C protein, a middle gene product of bacteriophage Mu, is the determinant of the transition from middle to late gene expression. C activates transcription from four late gene promoters, $P_{lys}$, $P_I$, $P_P$, and $P_{mom}$ by binding to a site overlapping their -35 elements. Site-specific, high-affinity binding of C to its recognition sequence results in both axial and torsional distortion of DNA at $P_{mom}$, which appears to play a role in recruitment of RNA polymerase to the promoter for mom gene transactivation. To identify the regions of C protein important for its function, deletion and site-directed mutagenesis were carried out. We demonstrate here that a helix-turn-helix (HTH) motif located toward the carboxy terminal end of the protein is the DNA-binding domain and amino acid residues involved in transactivation overlap the HTH motif. Mutagenesis studies also aided in the identification of the region important for dimerization. Structurebased sequence alignment and molecular modeling in conjunction with mutational analysis suggest that the HTH motif is part of a three-helix bundle, with remarkable similarity to paired (prd), a developmental regulatory protein from Drosophila. Additional key residues identified in the model to be crucial for C protein structure and DNA binding were shown to be important by mutagenesis. These results provide a structural framework for C function and insight into the mechanism of transactivation at the mom promoter.

Item Type: Journal Article
Publication: Proteins: Structure, Function, and Genetics
Publisher: Wiley-Liss
Additional Information: The copyright of this article belongs to Wiley-Liss, Inc.
Keywords: phage mu;helix-turn-helix;site-directed mutagenesis;paired protein;molecular modeling
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Division of Biological Sciences > Microbiology & Cell Biology
Date Deposited: 20 Nov 2007
Last Modified: 19 Sep 2010 04:12
URI: http://eprints.iisc.ac.in/id/eprint/398

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