DNA single-strand breaks (SSBs) containing covalent DNA-protein cross-links at 5'-termini (5'-DPCs) are produced from the C1'-oxidized abasic site, 2-deoxyribonolactone. These adducts need to be removed for SSB repair because 5'-phosphate is required for strand ligation. Prior studies showed that 5'-DPCs can undergo proteolysis by the 26S proteasome. However, how the remaining 5'-DNA-peptide cross-links (5'-DpCs) are removed is unclear. Herein, we found that a chemically synthesized and site-specific 5'-DpC can be repaired by HeLa cell nuclear extracts, and human flap-endonuclease 1 (hFEN1) plays an essential role in the DpC excision. We also synthesized a model 5'-DPC by reductive amination and showed that prior proteolysis of the cross-linked protein by trypsin greatly facilitated the DPC repair in HeLa cell nuclear extracts. Our findings suggest that 5'-DPCs within SSBs can be repaired by proteolysis followed by the long-patch base excision repair pathway.
Cepeda et al. (Mon,) studied this question.
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