Abstract
G-rich telomeric DNA sequences can form G-quadruplex structures. The heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) and a shortened derivative (UP1) are active in telomere length regulation, and it has been reported that UP1 can unwind G-quadruplex structures. Here, we investigate the interaction of hnRNP A1 with G-quadruplex DNA structures containing the human telomere repeat (TTAGGG) by gel retardation assays, ensemble fluorescence energy transfer (FRET) spectroscopy, and single molecule FRET microscopy. Our biochemical experiments show that hnRNP A1 binds well to the G-quadruplex telomeric DNA. Ensemble and single molecule FRET measurements provide further insight into molecular conformation: the telomeric DNA overhang is found to be in a folded state in the absence of hnRNP A1 and to remain predominantly in a compact state when complexed with hnRNP A1. This finding is in contrast to the previously reported crystal structures of UP1-telomere DNA complexes where the DNA oligo within the protein-DNA complex is in a fully open conformation.
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Acknowledgments
We would like to acknowledge financial support from the Lundbeck Foundation, the Danish Natural Science Research Council, and the Carlsberg Foundation. We are indepted to Thomas Schmidt and Jesper Donsmark for sharing with us some of their Matlab programs for data analysis.
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Krüger, A.C., Raarup, M.K., Nielsen, M.M. et al. Interaction of hnRNP A1 with telomere DNA G-quadruplex structures studied at the single molecule level. Eur Biophys J 39, 1343–1350 (2010). https://doi.org/10.1007/s00249-010-0587-x
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DOI: https://doi.org/10.1007/s00249-010-0587-x