Structure-forming CAG/CTG Repeats Interfere with Gap Repair to Cause Repeat Expansions and Chromosome Breaks

Overview

Journal Nat Commun

Specialty Biology

Date 2023 Apr 29

PMID 37120647

Authors

Erica J Polleys

Isabella Del Priore

James E Haber

Catherine H Freudenreich

Affiliations

Soon will be listed here.

Abstract

Expanded CAG/CTG repeats are sites of DNA damage, leading to repeat length changes. Homologous recombination (HR) is one cause of repeat instability and we hypothesized that gap filling was a driver of repeat instability during HR. To test this, we developed an assay such that resection and ssDNA gap fill-in would occur across a (CAG) or (CTG) repeat tract. When the ssDNA template was a CTG sequence, there were increased repeat contractions and a fragile site was created leading to large-scale deletions. When the CTG sequence was on the resected strand, resection was inhibited, resulting in repeat expansions. Increased nucleolytic processing by deletion of Rad9, the ortholog of 53BP1, rescued repeat instability and chromosome breakage. Loss of Rad51 increased contractions implicating a protective role for Rad51 on ssDNA. Together, our work implicates structure-forming repeats as an impediment to resection and gap-filling which can lead to mutations and large-scale deletions.

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