Interaction of YOYO-1 with guanine-rich DNA.

The oxazole homodimer YOYO-1 has served as a valuable tool for the detection and quantification of nucleic acids. While the base specificity and selectivity of binding of YOYO-1 has been researched to some extent, the effect of unorthodox nucleic acid conformations on dye binding has received relatively less attention. In this work, we attempt to correlate the quadruplex-forming ability of G-rich sequences with binding of YOYO-1. Oligonucleotides differing in the number of tandem G repeats, total length, and length of loop sequence were evaluated for their ability to form quadruplexes in presence of sodium (Na(+)) or potassium (K(+)) ions. The fluorescence behavior of YOYO-1 upon binding such G-rich sequences was also ascertained. A distinct correlation was observed between the strength and propensity of quadruplex formation, and the affinity of YOYO-1 to bind such sequences. Specifically, as exemplified by the oligonucleotides 5'-G4T2G4-3' and 5'-G3TG3TG3-3', sequences possessing longer G-rich regions and shorter loop sequences formed stronger quadruplexes in presence of K(+) which translated to weaker binding of YOYO-1. The dependence of binding of YOYO-1 on sequence and structural features of G-rich DNA has not been explored previously and such studies are expected to aid in more effective interpretation of applications involving the fluorophore.