DNA MODIFICATION BY METHYLTRANSFERASES

Enzymatic methylation of DNA plays important roles in both prokaryotes and eukaryotes. Structural study of the HhaI DNA methyltransferase has provided considerable insight into the chemistry of CS-cytosine methylation. The DNA-protein complex reveals a substrate cytosine flipped out of the double helix during the reaction, and a novel two-loop DNA-binding motif used for both sequence recognition and flipping the base. Structural comparison of HhaI C5-cytosine methyltransferase, TaqI NG-adenine methyltransferase, and catechol O-methyltransferase reveals a common catalytic domain structure, which might be universal among S-adenosyl-L-methionine (SAM)-dependent methyltransferases.