Role of folding kinetics of secondary structures in telomeric G-overhangs in the regulation of telomere maintenance inSaccharomyces cerevisiae

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Authors	JURIKOVA K. GAJARSKÝ Martin HAJIKAZEMI M. NOSEK J. PROCHAZKOVA K. PAESCHKE K. TRANTÍREK Lukáš TOMASKA L.
Year of publication	2020
Type	Article in Periodical
Magazine / Source	Journal of Biological Chemistry
MU Faculty or unit	Central European Institute of Technology
Citation
Web	https://www.jbc.org/article/S0021-9258(17)50320-8/pdf
Doi	http://dx.doi.org/10.1074/jbc.RA120.012914
Keywords	telomere; telomerase; Saccharomyces cerevisiae; cell cycle; Cdc13; G-hairpin; G-quadruplex; folding kinetics
Description	The ends of eukaryotic chromosomes typically contain a 3? ssDNA G-rich protrusion (G-overhang). This overhang must be protected against detrimental activities of nucleases and of the DNA damage response machinery and participates in the regulation of telomerase, a ribonucleoprotein complex that maintains telomere integrity. These functions are mediated by DNA-binding proteins, such as Cdc13 inSaccharomyces cerevisiae, and the propensity of G-rich sequences to form various non-B DNA structures. Using CD and NMR spectroscopies, we show here that G-overhangs ofS. cerevisiaeform distinct Hoogsteen pairing?based secondary structures, depending on their length. Whereas short telomeric oligonucleotides form a G-hairpin, their longer counterparts form parallel and/or antiparallel G-quadruplexes (G4s). Regardless of their topologies, non-B DNA structures exhibited impaired binding to Cdc13in vitroas demonstrated by electrophoretic mobility shift assays. Importantly, whereas G4 structures formed relatively quickly, G-hairpins folded extremely slowly, indicating that short G-overhangs, which are typical for most of the cell cycle, are present predominantly as single-stranded oligonucleotides and are suitable substrates for Cdc13. Using ChIP, we show that the occurrence of G4 structures peaks at the late S phase, thus correlating with the accumulation of long G-overhangs. We present a model of how time- and length-dependent formation of non-B DNA structures at chromosomal termini participates in telomere maintenance.
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