Detection of DNA Methyltransferase Activity via Fluorescence Resonance Energy Transfer and Exonuclease-Mediated Target Recycling

In this study, a sensitive method for detecting DNA methyltransferase (MTase) activity was developed by combining the effective fluorescence resonance energy transfer (FRET) of cationic conjugated polymers and exonuclease (Exo) III-mediated signal amplification. DNA adenine MTase targets the GATC sequence within a substrate and converts the adenine in this sequence into N6-methyladenine. In the method developed in this study, the methylated substrate is cleaved using Dpn I, whereby a single-stranded oligodeoxynucleotide (oligo) is released. Afterward, the oligo is hybridized to the 3' protruding end of the F-DNA probe to form a double-stranded DNA, which is then digested by Exo III. Subsequently, due to weak electrostatic interactions, only a weak FRET signal is observed. The introduction of the Exo-III-mediated target-recycling reaction improved the sensitivity for detecting MTase. This detection method was found to be sensitive for MTase detection, with the lowest detection limit of 0.045 U/mL, and was also suitable for MTase-inhibitor screening, whereby such inhibitors can be identified for disease treatment.