Abstract: F3g is a short DNA fragment, d(G3AG3T2G3A2G3), locating upstream of promoter E1 in the human proto-oncogenec-fms. Nuclear magnetic resonance (NMR) studies have revealed that, in near-physiological K+solutions, F3g folds into two distinct G-quadruplex structures with a spontaneous folding topology switch. Subsequent validations using a combination of techniques including NMR, CD, and PAGE have demonstrated that the kinetically favored Form 1 structure was a non-parallel two-tetrad G-quadruplex, while the thermodynamically stable Form 2 structure consisted of a stack of two parallel three-tetrad G-quadruplexes. These findings provided insights and a theoretical basis for further understanding the expression regulation of the human proto-oncogenec-fmsand the targeted treatment of related diseases.

Key words: human oncogenec-fms, DNA G-quadruplex, spontaneous structural switch, NMR, CD