Rudimentary G-quadruplex–based telomere capping in Saccharomyces cerevisiae

Abstract

Telomere capping conceals chromosome ends from exonucleases and checkpoints, but the full range of capping mechanisms is not well defined. Telomeres have the potential to form G-quadruplex (G4) DNA, although evidence for telomere G4 DNA function in vivo is limited. In budding yeast, capping requires the Cdc13 protein and is lost at nonpermissive temperatures in cdc13-1 mutants. Here, we use several independent G4 DNA–stabilizing treatments to suppress cdc13-1 capping defects. These include overexpression of three different G4 DNA binding proteins, loss of the G4 DNA unwinding helicase Sgs1, or treatment with small molecule G4 DNA ligands. In vitro, we show that protein-bound G4 DNA at a 3′ overhang inhibits 5′→3′ resection of a paired strand by exonuclease I. These findings demonstrate that, at least in the absence of full natural capping, G4 DNA can play a positive role at telomeres in vivo.

Understanding the stability of DNA G-quadruplex units in long human telomeric strands

“…In hypotrichous ciliates, telomeric 3 0 -overhangs form G4s that link together the gene-sized chromosomes of the macronucleus (for review [5]). In budding yeasts, G4s appear to be involved in telomere capping, at least when natural capping is impaired [6]. In mammalian cells, indirect evidence suggests that G4s may occur at telomeres during replication and at the 3 0 -overhangs, challenging telomere maintenance, at least in the absence of proteins able to unfold G4s or in the presence of ligands able to stabilize these structures [7e10].…”

Harnessing Nature’s Insights: Synthetic Small Molecules with Peroxidase‐Mimicking DNAzyme Properties

“…[20] To further confirm these results, we decided to perform similar experiments with another colorimetric substrate. On the basis of the work recently reported by Dong et al, [21,22] we selected 3,3',5,5'-tetramethylbenzidine sulfate (TMB). The oxidation of TMB is a two-step procedure, with a coloured intermediate that elicits UV/Vis maxima at 370 and 652 nm and a final product characterised by an absorbance maximum at 450 nm (Figure 3 A).…”

A Polymerase Theta-dependent repair pathway suppresses extensive genomic instability at endogenous G4 DNA sites

“…While guanine-rich single-stranded DNA can readily adopt such a structure in vitro, its in vivo formation has remained a subject of debate ever since the structure was first described 1 . Recent years have, however, seen a greatly increased interest in G-quadruplexes due to new insights into their possible roles in various biological processes such as gene expression, epigenetic regulation, telomere maintenance and DNA replication initiation [2][3][4][5][6][7][8] . While genome-wide in silico analyses have identified more than 300,000 G4 motifs (sites with G-quadruplex-forming potential) in the human genome 9 , perhaps the best in vivo evidence thus far for a functional role of G4 DNA comes from the bacterium Neisseria gonorrhoeae.…”