MutSα maintains the mismatch repair capability by inhibiting PCNA unloading.

Yoshitaka Kawasoe,Toshiki Tsurimoto,Hisao Masukata,Tatsuro S Takahashi,Takuro Nakagawa

doi:10.7554/elife.15155

Yoshitaka Kawasoe, Toshiki Tsurimoto + Show 3 more

Open Access

https://doi.org/10.7554/elife.15155

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Journal: eLife	Publication Date: Jul 12, 2016
Citations: 39	License type: CC BY 4.0

Affiliation: Kyushu University, Osaka University

Abstract

Eukaryotic mismatch repair (MMR) utilizes single-strand breaks as signals to target the strand to be repaired. DNA-bound PCNA is also presumed to direct MMR. The MMR capability must be limited to a post-replicative temporal window during which the signals are available. However, both identity of the signal(s) involved in the retention of this temporal window and the mechanism that maintains the MMR capability after DNA synthesis remain unclear. Using Xenopus egg extracts, we discovered a mechanism that ensures long-term retention of the MMR capability. We show that DNA-bound PCNA induces strand-specific MMR in the absence of strand discontinuities. Strikingly, MutSα inhibited PCNA unloading through its PCNA-interacting motif, thereby extending significantly the temporal window permissive to strand-specific MMR. Our data identify DNA-bound PCNA as the signal that enables strand discrimination after the disappearance of strand discontinuities, and uncover a novel role of MutSα in the retention of the post-replicative MMR capability.

Highlights

The evolutionarily conserved mismatch repair (MMR) system corrects replication errors post-replicatively to prevent their being fixed as mutations in the round of complementary DNA synthesis (Iyer et al, 2006; Jiricny, 2013; Kunkel and Erie, 2015)
We show that nucleoplasmic extract (NPE) of Xenopus eggs efficiently induces gap-directed, strand-specific MMR, whose capability remains even after sealing of the gap
The nucleoplasmic extract (NPE), a highly concentrated nuclear protein extract of Xenopus eggs, has been used as a powerful in vitro model system for DNA repair reactions coupled with DNA synthesis (Walter et al, 1998; Raschle et al, 2008; Olivera Harris et al, 2015)

Summary

Introduction

The evolutionarily conserved mismatch repair (MMR) system corrects replication errors post-replicatively to prevent their being fixed as mutations in the round of complementary DNA synthesis (Iyer et al, 2006; Jiricny, 2013; Kunkel and Erie, 2015). MMR is possible from the time of hemi-methylated GATC generation by DNA synthesis until full methylation of the GATC sites. Maintaining this temporal window is critical for efficient MMR, because over-expression of the Dam methylase, by which full-methylation of the GATC sites is accelerated, significantly elevates the mutation frequency (Herman and Modrich, 1981; Marinus et al, 1984). The E. coli MMR system can correct replication errors through a methylation-independent mechanism, where strand discontinuities can substitute for GATC methylation both in vivo and in vitro (Laengle-Rouault et al, 1986; Lahue et al, 1987; 1989)

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