Cancer Research Facility, Departments of Internal Medicine and Molecular Genetics & Microbiology, University of New Mexico Comprehensive Cancer Center, University of New Mexico Health Sciences Center, 915 Camino de Salud, 1 University of New Mexico, Albuquerque, NM, 87131, USA.
Division of Hematology and Medical Oncology, Department of Internal Medicine, Mayo Clinic, Jacksonville, FL, 32224, USA.
Sci Rep. 2023 Mar 16;13(1):4363. doi: 10.1038/s41598-023-31367-4.
DNA ligase I (LigI), the predominant enzyme that joins Okazaki fragments, interacts with PCNA and Pol δ. LigI also interacts with UHRF1, linking Okazaki fragment joining with DNA maintenance methylation. Okazaki fragments can also be joined by a relatively poorly characterized DNA ligase IIIα (LigIIIα)-dependent backup pathway. Here we examined the effect of LigI-deficiency on proteins at the replication fork. Notably, LigI-deficiency did not alter the kinetics of association of the PCNA clamp, the leading strand polymerase Pol ε, DNA maintenance methylation proteins and core histones with newly synthesized DNA. While the absence of major changes in replication and methylation proteins is consistent with the similar proliferation rate and DNA methylation levels of the LIG1 null cells compared with the parental cells, the increased levels of LigIIIα/XRCC1 and Pol δ at the replication fork and in bulk chromatin indicate that there are subtle replication defects in the absence of LigI. Interestingly, the non-replicative histone H1 variant, H1.0, is enriched in the chromatin of LigI-deficient mouse CH12F3 and human 46BR.1G1 cells. This alteration was not corrected by expression of wild type LigI, suggesting that it is a relatively stable epigenetic change that may contribute to the immunodeficiencies linked with inherited LigI-deficiency syndrome.
DNA 连接酶 I（LigI）是连接冈崎片段的主要酶，与 PCNA 和 Pol δ 相互作用。LigI 还与 UHRF1 相互作用，将冈崎片段的连接与 DNA 维持甲基化联系起来。冈崎片段也可以通过相对特征不明显的 DNA 连接酶 IIIα（LigIIIα）依赖性备份途径连接。在这里，我们研究了 LigI 缺乏对复制叉处蛋白质的影响。值得注意的是，LigI 缺乏并没有改变 PCNA 夹、前导链聚合酶 Pol ε、DNA 维持甲基化蛋白和核心组蛋白与新合成 DNA 的结合动力学。虽然复制和甲基化蛋白的缺失没有明显变化与 LIG1 缺失细胞与亲本细胞相比具有相似的增殖率和 DNA 甲基化水平一致，但复制叉处和大量染色质中 LigIIIα/XRCC1 和 Pol δ 的水平增加表明在没有 LigI 的情况下存在微妙的复制缺陷。有趣的是，非复制组蛋白 H1 变体 H1.0 在 LigI 缺乏的小鼠 CH12F3 和人 46BR.1G1 细胞的染色质中富集。这种改变不能通过表达野生型 LigI 来纠正，这表明它是一种相对稳定的表观遗传变化，可能导致与遗传性 LigI 缺乏综合征相关的免疫缺陷。
