biostudies-literatureUnknownCisneros-Aguirre MNCI NIH HHSA key step of Canonical Nonhomologous End Joining (C-NHEJ) is synapsis of DNA double strand break (DSB) ends for ligation. The DNA-PKcs dimer mediates synapsis in a long-range complex with DSB ends remaining apart, whereas the XLF homodimer can mediate synapsis in both long-range and short-range complexes. Recent structural studies found the PAXX homodimer may also facilitate synapsis in long-range complexes with DNA-PKcs via its interactions with Ku70. Thus, we examined the influence of PAXX in C-NHEJ of chromosomal DSBs, which we compared to another Ku-binding factor, MRI. Using EJ of blunt DSBs with Cas9 reporters as a readout for C-NHEJ, we found that PAXX and/or MRI are dispensable. However, when combined with disruption of DNA-PKcs, particularly with DNA-PKcs kinase inhibition, PAXX bioRxiv : the preprint server for biology2024.08.21.607864https://www.ebi.ac.uk/biostudies/studies/S-EPMC11370355biostudies-literatureDistinct functions of PAXX and MRI during chromosomal end joining.PMC11370355R01 CA240392P30 CA033572F99 CA284248R01 CA256989Ping XCisneros-Aguirre MLopezcolorado FWStark JMChen RfalseDistinct functions of PAXX and MRI during chromosomal end joining.A key step of Canonical Nonhomologous End Joining (C-NHEJ) is synapsis of DNA double strand break (DSB) ends for ligation. The DNA-PKcs dimer mediates synapsis in a long-range complex with DSB ends remaining apart, whereas the XLF homodimer can mediate synapsis in both long-range and short-range complexes. Recent structural studies found the PAXX homodimer may also facilitate synapsis in long-range complexes with DNA-PKcs via its interactions with Ku70. Thus, we examined the influence of PAXX in C-NHEJ of chromosomal DSBs, which we compared to another Ku-binding factor, MRI. Using EJ of blunt DSBs with Cas9 reporters as a readout for C-NHEJ, we found that PAXX and/or MRI are dispensable. However, when combined with disruption of DNA-PKcs, particularly with DNA-PKcs kinase inhibition, PAXX 2024-01-01T00:00:00Z2024 Aug2025-04-04T02:57:41.575Z2025-04-04T02:57:41.575ZS-EPMC113703553922909710.1101/2024.08.21.607864