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Proc Natl Acad Sci U S A. 1994 Nov 8;91(23):10957-61.

Three-dimensional structure of the adenine-specific DNA methyltransferase M.Taq I in complex with the cofactor S-adenosylmethionine.

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Institut für Kristallographie, Freie Universität, Berlin, Germany.


The Thermus aquaticus DNA methyltransferase M.Taq I (EC methylates N6 of adenine in the specific double-helical DNA sequence TCGA by transfer of --CH3 from the cofactor S-adenosyl-L-methionine. The x-ray crystal structure at 2.4-A resolution of this enzyme in complex with S-adenosylmethionine shows alpha/beta folding of the polypeptide into two domains of about equal size. They are arranged in the form of a C with a wide cleft suitable to accommodate the DNA substrate. The N-terminal domain is dominated by a nine-stranded beta-sheet; it contains the two conserved segments typical for N-methyltransferases which form a pocket for cofactor binding. The C-terminal domain is formed by four small beta-sheets and alpha-helices. The three-dimensional folding of M.Taq I is similar to that of the cytosine-specific Hha I methyltransferase, where the large beta-sheet in the N-terminal domain contains all conserved segments and the enzymatically functional parts, and the smaller C-terminal domain is less structured.

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