期刊
BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS
卷 1840, 期 1, 页码 41-52出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbagen.2013.08.028
关键词
G-quadruplex; i-Motif; Quadruplex/duplex competition; n-myc; Chromatography; Multivariate analysis
资金
- Spanish government [CTQ2012-38616-C02-02, CTQ2010-20541-C03-01]
Background: Cytosine- and guanine-rich regions of DNA are capable of forming complex structures named i-motifs and G-quadruplexes, respectively. In the present study the solution equilibria at nearly physiological conditions of a 34-base long cytosine-rich sequence and its complementary guanine-rich strand corresponding to the first intron of the n-myc gene were studied. Both sequences, not yet studied, contain a 12-base tract capable of forming stable hairpins inside the i-motif and G-quadruplex structures, respectively. Methods: Spectroscopic, mass spectrometry and separation techniques, as well as multivariate data analysis methods, were used to unravel the species and conformations present. Results: The cytosine-rich sequence forms two i-motifs that differ in the protonation of bases located in the loops. A stable Watson-Crick hairpin is formed by the bases in the first loop, stabilizing the i-motif structure. The guaninerich sequence adopts a parallel G-quadruplex structure that is stable throughout the pH range 3-7, despite the protonation of cytosine and adenine bases at lower pH values. The presence of G-quadruplex aggregates was confirmed using separation techniques. When mixed, G-quadruplex and i-motif coexist with the Watson-Crick duplex across a pH range from approximately 3.0 to 6.5. Conclusions: Two cytosine- and guanine-rich sequences in n-myc gene may form stable i-motif and G-quadruplex structures even in the presence of long loops. pH modulates the equilibria involving the intramolecular structures and the intermolecular Watson-Crick duplex. General significance: Watson-Crick hairpins located in the intramolecular G-quadruplexes and i-motifs in the promoter regions of oncogenes could play a role in stabilizing these structures. (C) 2013 Elsevier B.V. All rights reserved.
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