Streamlining effects of extra telomeric repeat on telomeric DNA folding revealed by fluorescence-force spectroscopy. Issue 21 (16th October 2019)

• Record Type: Journal Article
• Authors: Mitra, Jaba; Ha, Taekjip
• Is Part Of: Nucleic acids research. Volume 47:Issue 21(2019)
• Page Start: 11044
• Page End: 11056
• Publication Date: 2019-10-16
• Subjects: Nucleic acids -- Periodicals; Molecular biology -- Periodicals; 572.805
• DOI: 10.1093/nar/gkz906
• Languages: English
• ISSNs: 0305-1048

Abstract

Abstract: A human telomere ends in a single-stranded 3′ tail, composed of repeats of T2 AG3 . G-quadruplexes (GQs) formed from four consecutive repeats have been shown to possess high-structural and mechanical diversity. In principle, a GQ can form from any four repeats that are not necessarily consecutive. To understand the dynamics of GQs with positional multiplicity, we studied five and six repeats human telomeric sequence using a combination of single molecule FRET and optical tweezers. Our results suggest preferential formation of GQs at the 3′ end both in K + and Na + solutions, with minor populations of 5′-GQ or long-loop GQs. A vectorial folding assay which mimics the directional nature of telomere extension showed that the 3′ preference holds even when folding is allowed to begin from the 5′ side. In 100 mM K +, the unassociated T2 AG3 segment has a streamlining effect in that one or two mechanically distinct species was observed at a single position instead of six or more observed without an unassociated repeat. We did not observe such streamlining effect in 100 mM Na + . Location of GQ and reduction in conformational diversity in the presence of extra repeats have implications in telomerase inhibition, T-loop formation and telomere end protection.