The 9-1-1 checkpoint clamp stimulates DNA resection by Dna2-Sgs1 and Exo1.

Greg H.P. Ngo,David Lydall,Judith L. Campbell,Lata Balakrishnan,Marion Dubarry

doi:10.1093/nar/gku746

Abstract

Single-stranded DNA (ssDNA) at DNA ends is an important regulator of the DNA damage response. Resection, the generation of ssDNA, affects DNA damage checkpoint activation, DNA repair pathway choice, ssDNA-associated mutation and replication fork stability. In eukaryotes, extensive DNA resection requires the nuclease Exo1 and nuclease/helicase pair: Dna2 and Sgs1BLM. How Exo1 and Dna2-Sgs1BLM coordinate during resection remains poorly understood. The DNA damage checkpoint clamp (the 9-1-1 complex) has been reported to play an important role in stimulating resection but the exact mechanism remains unclear. Here we show that the human 9-1-1 complex enhances the cleavage of DNA by both DNA2 and EXO1 in vitro, showing that the resection-stimulatory role of the 9-1-1 complex is direct. We also show that in Saccharomyces cerevisiae, the 9-1-1 complex promotes both Dna2-Sgs1 and Exo1-dependent resection in response to uncapped telomeres. Our results suggest that the 9-1-1 complex facilitates resection by recruiting both Dna2-Sgs1 and Exo1 to sites of resection. This activity of the 9-1-1 complex in supporting resection is strongly inhibited by the checkpoint adaptor Rad953BP1. Our results provide important mechanistic insights into how DNA resection is regulated by checkpoint proteins and have implications for genome stability in eukaryotes.

Highlights

DNA resection, the nucleolytic degradation of one strand of DNA ends, has emerged as an important regulator of the DNA damage response [1,2]
We examined the effect of 9-1-1 on DNA2 and EXO1 activity, the two nucleases involved in long-range resection
We found that DNA2 cleaved this substrate efficiently (Figure 1A, lanes 2–4)

Summary

Introduction

DNA resection, the nucleolytic degradation of one strand of DNA ends, has emerged as an important regulator of the DNA damage response [1,2]. The substrates for resection, DNA ends, arise at uncapped telomeres, DNA double strand breaks (DSBs) and stalled replication forks. DNA resection generates single-stranded DNA (ssDNA) to trigger and maintain DNA damage checkpoint signaling, which induces cell cycle arrest, senescence (permanent cell cycle arrest) or apoptosis (cell death) [3,4]. Unregulated resection activities degrade stalled replication forks or dysfunctional telomeres [9,10,11,12,13]. Proper regulation of DNA resection has important consequences on genome stability and cell viability

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Conclusion