# DNA end processing by the Mre11/Rad50/Nbs1 complex in human cells

> **NIH NIH R01** · UNIVERSITY OF TEXAS AT AUSTIN · 2022 · $311,618

## Abstract

Double-strand breaks in DNA are a lethal form of genome damage that can also lead to large-
scale chromosomal rearrangements and deletions when mis-repaired. Non-homologous end
joining and homologous recombination are the two major pathways of DNA double-strand break
repair in eukaryotes, and the decision between these pathways can have long-lasting
consequences for cell fate. Current models of DNA repair suggest that non-homologous and
homologous recombination factors compete with each other for end binding, processing, and
repair in a manner that favors homologous recombination during the S and G2 phases of the cell
cycle, but this competition is still ill-defined despite many years of study. Here we build upon our
recent results showing that the Mre11-Rad50-Nbs1 (MRN) complex performs end processing in
physiological conditions that depends on the core non-homologous end joining complex, DNA-
dependent protein kinase (DNA-PK). Ensemble biochemistry, single-molecule experiments, and
quantitation of DNA repair intermediates in human cells shows that MRN-mediated end
processing occurs at DNA-PK-bound ends, promoted by the cell cycle-regulated repair factor
CtIP. These results suggest that DNA double-strand break repair "choice" is not a competition,
but rather a sequential and ordered process from non-homologous to homologous pathways. To
validate these results and understand double-strand break recognition and processing at a
mechanistic level, we propose to further investigate the characteristics of DNA end processing
globally in human cells. We will test our hypotheses by analyzing the regulation of DNA end
processing by by Mre11 nuclease activity and CtIP modifications, and will examine the
characteristics of DNA end processing as it occurs in non-cycling cells. Lastly, we will
investigate the structural biology of the cooperative, multi-subunit end repair complex that MRN
forms with DNA-PK on DNA ends, with both recombinant proteins as well as native complexes
from human cells. These experiments will further establish novel methods for characterizing
DNA repair intermediates and solidify a new paradigm in DNA double-strand break repair that
mechanistically links non-homologous end joining with the initiation of homologous
recombination.

## Key facts

- **NIH application ID:** 10415125
- **Project number:** 5R01GM138548-02
- **Recipient organization:** UNIVERSITY OF TEXAS AT AUSTIN
- **Principal Investigator:** TANYA T PAULL
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $311,618
- **Award type:** 5
- **Project period:** 2021-06-01 → 2025-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10415125

## Citation

> US National Institutes of Health, RePORTER application 10415125, DNA end processing by the Mre11/Rad50/Nbs1 complex in human cells (5R01GM138548-02). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10415125. Licensed CC0.

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