title: G-quadruplex hinders translocation of BLM helicase on DNA: a real-time fluorescence spectroscopic unwinding study and comparison with duplex substrates.
abstract: Sequences with the potential to form G-quadruplex structures are spread throughout genomic DNA. G-quadruplexes in promoter regions can play regulatory roles in gene expression. Expression of protein-encoding genes involves processing of DNA and RNA molecules at the level of transcription and translation, respectively. In order to examine how the G-quadruplex affects processing of nucleic acids, we established a real-time fluorescent assay and studied the unwinding of intramolecular G-quadruplex formed by the human telomere, ILPR and PSMA4 sequences by the BLM helicase. Through comparison with their corresponding duplex substrates, we found that the unwinding of intramolecular G-quadruplex structures was much less efficient than that of the duplexes. This result is in contrast to previous reports that multistranded intermolecular G-quadruplexes are far better substrates for the BLM and other RecQ family helicases. In addition, the unwinding efficiency varied significantly among the G-quadruplex structures, which correlated with the stability of the structures. These facts suggest that G-quadruplex has the capability to modulate the processing of DNA and RNA molecules in a stability-dependent manner and, as a consequence, may provide a mechanism to play regulatory roles in events such as gene expression.
authors.affiliation: Laboratory of Biochemistry and Biophysics, College of Life Sciences, Wuhan University, Wuhan 430072, PR China.
authors.forename: Jia-quan
authors.initials: JQ
authors.lastname: Liu
authors.forename: Chang-yue
authors.initials: CY
authors.lastname: Chen
authors.forename: Yong
authors.initials: Y
authors.lastname: Xue
authors.forename: Yu-hua
authors.initials: YH
authors.lastname: Hao
authors.forename: Zheng
authors.initials: Z
authors.lastname: Tan
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000378:metabolism*; D054856:G-Quadruplexes; D006801:Humans; D053484:RecQ Helicases / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D016615:Telomere / Q000737:chemistry / Q000378:metabolism*; D014178:Translocation, Genetic
chemical_list: D004247:DNA; D053484:RecQ Helicases