Mg²⁺ mediated sequence-specific binding of transcriptional activator protein C of bacteriophage Mu to DNA

Abstract

The contributions from the secondary structure of the transcriptional activator protein C of bacteriophage Mu to its specific DNA binding and the influence of various factors, viz., electrolytes, and minor groove and major groove binders on this protein-DNA interaction have been addressed. Circular dichroism (CD) spectral results suggest that, in the absence of Mg²⁺, C protein exhibits a β-pleated sheetlike structure and Mg²⁺ changes the conformation to a more α-helical structure which could provide specific geometrical constraints complementary to those of DNA helix. Thus, Mg²⁺ acts as a cofactor for the binding of the C protein to its specific site in DNA by inducing conformational changes in the protein. Competitive binding studies with minor and major groove binding drugs, viz., distamycin A and methyl green, respectively, and the DMS footprinting data indicate that the C protein recognizes the major groove of DNA during complex formation. Further, upon major groove binding, C protein brings about changes in DNA conformation; such conformational changes could have implications in the transcription process.