Accelerated assembly of G-quadruplex structures by a small molecule

In the presence of alkali cations, notably potassium and sodium, DNA oligomers that possess two G-rich repeats associate into either a tetrameric parallel G-quadruplex or a variety of dimeric antiparallel G-quadruplexes. The formation of such structures is normally a very slow process. Some proteins, such as the beta-subunit of the Oxytricha telomere-binding protein, promote the formation of G-quadruplex structures in a chaperone-like manner. In this report, we present data concerning the role of a perylene derivative, PIPER, in the assembly of G-quadruplex structures as the first example of a small ligand behaving as a driver in the assembly of polynucleotide secondary structures. Gel-shift experiments demonstrate that PIPER can dramatically accelerate the association of a DNA oligomer containing two tandem repeats of the human telomeric sequence (TTAGGG) into di- and tetrameric G-quadruplexes. In so doing, PIPER alters the oligomer dimerization kinetics from second to first order. The presence of 10 mu M PIPER accelerates the assembly of varied dimeric G-quadruplexes an estimated 100-fold from 2 mu M oligomer, These results imply that some biological effects elicited by G-quadruplex-interactive agents, such as the induction of anaphase bridges, may stem from the propensity such compounds have for assembling G-quadruplexes.