Structural basis of novel quadruplex-duplex switching of nucleic acids

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The novel quadruplex and duplex structures of d(GGAGGA), formed in the presence and absence of potassium ions, respectively, were determined by NMR.It is notable that the duplex structure is composed exclusively of non-standard G : G and A : A basepairs.It was found for the first time that the RNA-binding protein, hnRNP D0 has the ability to transform the quadruplex structure to a single-stranded form. The structures and interactions with RNA of hnRNP DO and the related protein, Musashi1, were determined by NMR.It was suggested that this unique activity may be related to the maintenance of the telomere.The structure of the novel antitumor drug, UCH9, complexed with DNA was determined by NMR.The B-form to A-form structural transition caused by drug-binding was identified, and its biological significance was implied.