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Updated: Jun 8, 2026

Using Next Generation Sequencing to Identify Mutations Associated with Repair of a CAS9-induced Double Strand Break Near the CD4 Promoter
Published on: March 31, 2022
Dual modes of interaction between XRCC4 and polynucleotide kinase/phosphatase: implications for nonhomologous end
Rajam S Mani1, Yaping Yu, Shujuan Fang
1Department of Oncology, University of Alberta, Alberta, and the Cross Cancer Institute, Edmonton, Alberta T6G 1Z2, Canada.
Abstract:
XRCC4 plays a crucial role in the nonhomologous end joining (NHEJ) pathway of DNA double-strand break repair acting as a scaffold protein that recruits other NHEJ proteins to double-strand breaks. Phosphorylation of XRCC4 by protein kinase CK2 promotes a high affinity interaction with the forkhead-associated domain of the end-processing enzyme polynucleotide kinase/phosphatase (PNKP). Here we reveal that unphosphorylated XRCC4 also interacts with PNKP through a lower affinity interaction site within the catalytic domain and that this interaction stimulates the turnover of PNKP. Unexpectedly, CK2-phosphorylated XRCC4 inhibited PNKP activity. Moreover, the XRCC4·DNA ligase IV complex also stimulated PNKP enzyme turnover, and this effect was independent of the phosphorylation of XRCC4 at threonine 233. Our results reveal that CK2-mediated phosphorylation of XRCC4 can have different effects on PNKP activity, with implications for the roles of XRCC4 and PNKP in NHEJ.
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