DNA bending facilitates the error-free DNA damage tolerance pathway and upholds genome integrity

DNA replication is sensitive to damage in the template. To bypass lesions and complete replication, cells activate recombination‐mediated (error‐free) and translesion synthesis‐mediated (error‐prone) DNA damage tolerance pathways. Crucial for error‐free DNA damage tolerance is template switching, which depends on the formation and resolution of damage‐bypass intermediates consisting of sister chromatid junctions. Here we show that a chromatin architectural pathway involving the high mobility group box protein Hmo1 channels replication‐associated lesions into the error‐free DNA damage tolerance pathway mediated by Rad5 and PCNA polyubiquitylation, while preventing mutagenic bypass and toxic recombination. In the process of template switching, Hmo1 also promotes sister chromatid junction formation predominantly during replication. Its C‐terminal tail, implicated in chromatin bending, facilitates the formation of catenations/hemicatenations and mediates the roles of Hmo1 in DNA damage tolerance pathway choice and sister chromatid junction formation. Together, the results suggest that replication‐associated topological changes involving the molecular DNA bender, Hmo1, set the stage for dedicated repair reactions that limit errors during replication and impact on genome stability. Synopsis The DNA‐bending HMG‐box protein Hmo1 channels replication‐associated lesions into error‐free template switching pathways, highlighting the regulatory roles of chromosome architecture upstream of more dedicated repair mechanisms. Replication‐associated topological changes foster error‐free damage‐bypass. The Rad5‐mediated error‐free damage‐bypass is activated by topological changes in S phase. The chromatin architectural protein Hmo1 prevents mutagenic bypass and toxic recombination. Hmo1‐mediated DNA bending promotes error‐free DNA damage tolerance. Graphical Abstract The DNA‐bending HMG‐box protein Hmo1 channels replication‐associated lesions into error‐free template switching pathways, highlighting the regulatory roles of chromosome architecture upstream of more dedicated repair mechanisms.