G-quadruplex-forming GGA repeat region functions as a negative regulator of the enhancer.

An enhancer located upstream of the transcriptional start site of containing two GGA-rich regions and a 14-GGA repeat (GGA) region has been previously identified. Three copies of four GGA repeats in the promoter that form a tetrad:heptad:heptad:tetrad (T:H:H:T) dimerized G-quadruplex (G4) structure reportedly functions as both a transcriptional repressor and activator. Here, the secondary structures of the two GGA-rich and (GGA) regions were analyzed using circular dichroism spectral analysis, which indicated that the two GGA-rich DNAs formed parallel-type G4 structures, whereas (GGA) DNA formed the T:H:H:T dimerized G4 structure.