Mgs1 function at G-quadruplex structures during DNA replication

Katrin Paeschke,Peter Burkovics

doi:10.1007/s00294-020-01128-1

Abstract

The coordinated action of DNA polymerases and DNA helicases is essential at genomic sites that are hard to replicate. Among these are sites that harbour G-quadruplex DNA structures (G4). G4s are stable alternative DNA structures, which have been implicated to be involved in important cellular processes like the regulation of gene expression or telomere maintenance. G4 structures were shown to hinder replication fork progression and cause genomic deletions, mutations and recombination events. Many helicases unwind G4 structures and preserve genome stability, but a detailed understanding of G4 replication and the re-start of stalled replication forks around formed G4 structures is not clear, yet. In our recent study, we identified that Mgs1 preferentially binds to G4 DNA structures in vitro and is associated with putative G4-forming chromosomal regions in vivo. Mgs1 binding to G4 motifs in vivo is partially dependent on the helicase Pif1. Pif1 is the major G4-unwinding helicase in S. cerevisiae. In the absence of Mgs1, we determined elevated gross chromosomal rearrangement (GCR) rates in yeast, similar to Pif1 deletion. Here, we highlight the recent findings and set these into context with a new mechanistic model. We propose that Mgs1's functions support DNA replication at G4-forming regions.

Highlights

Precise replication of the genome is essential for most eukaryotic cells, as it determines the fate of the daughter cells
We demonstrated that Mgs1’s function at G4 structures is essential for genome stability and that G4 structures that lack Mgs1 caused increased gross chromosomal rearrangement (GCR), accumulation of γH2A as well as slow growth
The current model is that G4 structures, which form during DNA replication, lead to a slowing down of the replication fork as it approaches the G4 structure (Paeschke et al 2011)

Summary

Introduction

Precise replication of the genome is essential for most eukaryotic cells, as it determines the fate of the daughter cells. All of these functions are linked to the preservation of genome stability: (I.) Pif1 activity is essential for the maintenance of the mitochondrial genome (Foury and Dyck 1985), (II.) Pif1 cooperates with proteins of the replication machinery (Dna2 and PCNA) (Budd et al 2006; Buzovetsky et al 2017) and supports Okazaki-fragment maturation (Stith et al 2008; Pike et al 2009), (III.) Pif1 co-localizes with DNA repair foci and suppresses the accumulation of toxic DNA recombination intermediates (Wagner et al 2006; Wilson et al 2013), (IV.) Pif1 maintains the replication fork barrier at the ribosomal DNA loci, (Ivessa et al 2000), (V.) Pif1 negatively regulates telomerase (Schulz and Zakian 1994; Boule et al 2005; Phillips et al 2015) and (VI.) Pif1 is associated with putative G4-forming regions in the yeast genome.

Results

Conclusion