The long range goal of this project is to develop an understanding of the interactions that occur between DNA and proteins in solution which result in the formation of highly specific complexes that perform a variety of specific functions. The project will focus on methyltransferases and their interaction with target DNA. Methylation performs many functions ranging from the protection of host DNA against bacterial restriction endonucleases to the regulation of gene expression in eukaryotes. The experiments are focused on one of the most characterized methyltransferases, EcoRI methyltransferase, which uses the cofactor S- adenosylmethionine to methylate the central adenine in the canonical site 5'GAATTC3'. There is considerable evidence that the structure of both the DNA and the methyltransferase are distorted when the complex is formed. The distortions are likely to add specificity to the formation of the complex. The nature of the distortions and the forces that are required to cause them have not been determined. The techniques of transient electric birefringence and optical Kerr effect will be used to characterize the mechanical and electrical properties of the methyltransferase and the DNA, separately and in a ternary complex with a cofactor analog. We will determine the changes in shape and mechanical stiffness of the methyltransferase upon the addition of cofactors. We will determine the angle of the putative bend that is induced in the DNA and the relative position of the methyltransferase. The results will be compared with those for other DNA-protein complexes with an aim of developing a physical model to explain the interactions in solution. The mechanical properties of the methyltransferase will be compared with other proteins of similar size that are believed to have elastic hinges between their domains.
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