Sequence-specific methyltransferase-induced labeling of DNA (SMILing DNA).

A new concept for sequence-specific labeling of DNA by using chemically modified cofactors for DNA methyltransferases is presented. Replacement of the amino acid side chain of the natural cofactor S-adenosyl-L-methionine with an aziridine group leads to a cofactor suitable for DNA methyltransferase-catalyzed sequence-specific coupling with DNA. Sequence-specifically fluorescently labeled plasmid DNA was obtained by using the DNA methyltransferase from Thermus aquaticus (M.TaqI) as catalyst and attaching a fluorophore to the aziridine cofactor. First results suggest that all classes of DNA methyltransferases with different recognition sequences can be used. In addition, this novel method for DNA labeling should be applicable to a wide variety of reporter groups.