Putative G-quadruplex sequences spread throughout the genome of human and other species. G-quadruplex structures are believed to play roles in important biological processes, such as regulation of gene expression and maintenance of genome stability. How G-quadruplexes affect the processing of DNA and RNA in various physiological events, such as transcription and translation, is an important question deserving exploration. Recently, TAN Zheng's team established a fluorescent method to monitor the kinetics of intramolecular G-quadruplex unwinding in real-time. Using this method they studied the unwinding of intramolecular G-quadruplex from the human telomere, ILPR and PSMA4 sequences by the BLM helicase and compared it with the unwinding of their corresponding duplex substrates. Their study revealed that the unwinding of the G-quadruplex structures is significantly less efficient than that of the duplexes. In addition, their data show that the efficiency of G-quadruplex unwinding reversibly correlates with quadruplex stability. These results imply that G-quadruplex can create a barrier to processes such as protein translocation on nucleic acids that may have implication in modulating the opening/annealing of genomic DNA.

Refer to: Liu JQ, Chen CY, Xue Y, Hao YH, Tan Z. 2010. G-Quadruplex Hinders Translocation of BLM Helicase on DNA: A Real-Time Fluorescence Spectroscopic Unwinding Study and Comparison with Duplex Substrates. J Am Chem Soc . 132(30): 10521-10527. DOI: 10.1021/ja1038165). This work was supported by Grants from MSTC and NSFC.