the screening of G-quadruplex ligands Oscar Mendoza1,2,*, Nassima Meriem Gueddouda1,2, Jean-Baptiste Boulé3,

Helicases, enzymes that unwind DNA or RNA struc-ture, are present in the cell nucleus and in the mito-chondrion. Although the majority of the helicases un-wind DNA or RNA duplexes, some of these proteins are known to resolve unusual structures such as G-quadruplexes (G4) in vitro. G4 may form stable bar-rier to the progression of molecular motors tracking on DNA. Monitoring G4 unwinding by these enzymes may reveal the mechanisms of the enzymes and pro-vides information about the stability of these struc-tures. In the experiments presented herein, we devel-oped a reliable, inexpensive and rapid fluorescence-based technique to monitor the activity of G4 heli-cases in real time in a 96-well plate format. This sys-tem was used to screen a series of G4 structures and G4 binders for their effect on the Pif1 enzyme, a 5 ′ to 3 ′ DNA helicase. This simple assay should be adapt-able to analysis of other helicases and G4 structures