# ERCC6L2 ensures repair fidelity for staggered-end DNA double-strand breaks

## TL;DR

This study identifies ERCC6L2 as a key protein that helps repair specific types of DNA breaks caused by genome editing tools like Cas12a.

## Contribution

ERCC6L2 is newly identified as critical for accurate repair of staggered DNA breaks but not blunt-ended breaks.

## Key findings

- ERCC6L2 prevents large deletions and translocations from staggered DNA breaks caused by Cas12a, TALENs, or dual Cas9 nicks.
- Loss of ERCC6L2 makes cells more sensitive to staggered DNA breaks from Cas12a or etoposide.
- ERCC6L2 counteracts MRN-mediated resection by binding and melting staggered DNA ends.

## Abstract

DNA double-strand breaks (DSBs) both pose threats to genome integrity and are commonly used for genome editing applications. Structural features of DSB ends play key roles in determining DNA repair pathway usage and outcomes during genome editing, but the cellular factors involved in these processes are only partially known. Through genome-wide CRISPRi screening, we identify ERCC6L2 as critical for repairing Cas12a-induced staggered DSBs but irrelevant for Cas9-induced blunt DSBs. We show that ERCC6L2 acts as a protection factor for staggered DSBs with either 5′ or 3′ polarity, preventing large deletions and translocations stemming from DNA damage induced by Cas12a, TALENs, or dual Cas9 nicks. Furthermore, ERCC6L2 loss hyper-sensitizes cells to multiple staggered DSBs induced by promiscuous Cas12a activity or etoposide-induced TOP2 trapping. By combining genetics and biochemical reconstitution, we find that ERCC6L2 counteracts MRE11-RAD50-NBS1 (MRN)-mediated resection by binding and melting staggered DNA ends, thereby promoting accurate end joining. Our data reveal a protective role of ERCC6L2 in staggered-end DSB repair, which suggests the molecular underpinnings of pathology in patients with ERCC6L2 mutations and cautions against using overhang-inducing genome editing tools for their treatment.

Structural features of DNA double-strand break (DSB) ends play key roles in determining DNA repair pathway usage and outcomes. Here, the authors identify ERCC6L2, a poorly characterized ATPase, as playing a minimal role in blunt end DSB repair but crucial for repair of staggered end DSBs.