Genomic integrity is threatened by cytotoxic DNA double-strand breaks (DSBs), which must be resolved efficiently to prevent sequence loss, chromosomal rearrangements/translocations, or cell death. Polymerase μ (Polμ) participates in DSB repair via the nonhomologous end-joining (NHEJ) pathway, by filling small sequence gaps in broken ends to create substrates ultimately ligatable by DNA Ligase IV. Here we present structures of human Polμ engaging a DSB substrate. Synapsis is mediated solely by Polμ, facilitated by single-nucleotide homology at the break site, wherein both ends of the discontinuous template strand are stabilized by a hydrogen bonding network. The active site in the quaternary Pol μ complex is poised for catalysis and nucleotide incoporation proceeds in crystallo. These structures demonstrate that Polμ may address complementary DSB substrates during NHEJ in a manner indistinguishable from single-strand breaks.

基因组完整性受到细胞毒性 DNA 双链断裂 (DSB) 的威胁，必须有效解决，以防止序列丢失、染色体重排/易位或细胞死亡。聚合酶 μ (Polμ) 通过非同源末端连接 (NHEJ) 途径参与 DSB 修复，通过填充断端中的小序列间隙来创建最终可由 DNA 连接酶 IV 连接的底物。在这里，我们展示了与 DSB 底物结合的人类 Polμ 结构。突触仅由 Polμ 介导，由断裂位点的单核苷酸同源性促进，其中不连续模板链的两端由氢键网络稳定。四元 Pol μ 复合物中的活性位点准备好进行催化，并在晶体中进行核苷酸掺入。