Inhibition of unwinding of G-quadruplex structures by Sgs1 helicase in thepresence of N,N '-bis[2-(1-piperidino)ethyl]-3,4,9,10-perylenetetracarboxylic diimide, a G-quadruplex-interactive ligand

N,N'-Bis[2-(1-piperidino)ethyl]-3,4,9,10-perylenetetracarboxylic diimide (P IPER), a perylene derivative, is a very potent and selective G-quadruplex D NA-interactive agent. It has been shown to inhibit DNA polymerase and telom erase by stacking externally to the G-tetrads in the G-quadruplex structure s. Recently, we have demonstrated that this small molecule greatly accelera tes the assembly of G-quadruplex structures in a cell-free system. In this report, we present data demonstrating that PIPER prevents the unwinding of G-quadruplex structures by yeast Sgs1 helicase. Sgs1 belongs to the RecQ DN A helicase family whose members include other G-quadruplex DNA unwinding he licases, such as human Bloom's syndrome and human Werner's syndrome helicas es. PIPER specifically prevents the unwinding of G-quadruplex DNA but not d uplex DNA by Sgs1. Competition experiments indicate that this inhibitory ac tivity is due to the interaction of PIPER with G-quadruplex structures rath er than the helicase itself. These results combined with previous studies s uggest a possible mechanism of action for these G-quadruplex-interactive ag ents inside cells: they might induce G-quadruplex formation in G-rich regio ns on genomic DNA, stabilize these structures, and prevent them from being cleared by enzymes such as helicases. The G-quadruplex structures may, in t urn, disrupt some critical cellular events such as DNA replication, transcr iption regulation, and telomere maintenance.