Fluorescent molecular rotors detect O 6 -methylguanine dynamics and repair in duplex DNA.

Alkylation at the O 6 position of guanine is a common and highly mutagenic form of DNA damage. Direct repair of O 6 -alkylguanines by the "suicide" enzyme O 6 -methylguanine DNA methyltransferase (MGMT, AGT, AGAT) maintains genome stability and inhibits carcinogenesis. In this study, a fluorescent analogue of thymidine containing trans -stilbene ( ts T) is quenched by O 6 -methylguanine residues in the opposite strand of DNA by molecular dynamics that propagate through the duplex with as much as ∼9 Å of separation. Increased fluorescence of ts T or the cytosine analogue ts C resulting from MGMT-mediated DNA repair were distinguishable from non-covalent DNA-protein binding following protease digest. To our knowledge, this is the first study utilizing molecular rotor base analogues to detect DNA damage and repair activities in duplex DNA.