Translesion polymerase eta both facilitates DNA replication and promotes increased human genetic variation at common fragile sites

Shyam Twayana, Albino Bacolla, Angelica Barreto-Galvez, Ruth B. De-Paula, William C. Drosopoulos, Settapong T. Kosiyatrakul, Eric E. Bouhassira, John A. Tainer, Advaitha Madireddy, Carl L. Schildkraut

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Common fragile sites (CFSs) are difficult-to-replicate genomic regions that form gaps and breaks on metaphase chromosomes under replication stress. They are hotspots for chromosomal instability in cancer. Repetitive sequences located at CFS loci are inefficiently copied by replicative DNA polymerase (Pol) delta. However, translesion synthesis Pol eta has been shown to efficiently polymerize CFS-associated repetitive sequences in vitro and facilitate CFS stability by a mechanism that is not fully understood. Here, by locus-specific, single-molecule replication analysis, we identified a crucial role for Pol eta (encoded by the gene POLH) in the in vivo replication of CFSs, even without exogenous stress. We find that Pol eta deficiency induces replication pausing, increases initiation events, and alters the direction of replication-fork progression at CFSFRA16D in both lymphoblasts and fibroblasts. Furthermore, certain replication pause sites at CFS-FRA16D were associated with the presence of non-B DNA-forming motifs, implying that non-B DNA structures could increase replication hindrance in the absence of Pol eta. Further, in Pol eta-deficient fibroblasts, there was an increase in fork pausing at fibroblast-specific CFSs. Importantly, while not all pause sites were associated with non-B DNA structures, they were embedded within regions of increased genetic variation in the healthy human population, with mutational spectra consistent with Pol eta activity. From these findings, we propose that Pol eta replicating through CFSs may result in genetic variations found in the human population at these sites.

Original languageEnglish (US)
Article numbere2106477118
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number48
StatePublished - Nov 30 2021
Externally publishedYes


  • Common fragile sites
  • Non-B DNA
  • Polymerase eta
  • Replication fork pause
  • SNP

ASJC Scopus subject areas

  • General


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