Nayak Ashok R, Sokolova Viktoriia, Sillamaa Sirelin, Herbine Karl, Sedman Juhan, Temiakov Dmitry
Department of Biochemistry and Molecular Biology, Thomas Jefferson University; 1020 Locust St, Philadelphia, USA.
Institute of Molecular and Cell Biology, University of Tartu, Riia 23, Tartu, Estonia.
Nat Commun. 2025 Mar 11;16(1):2417. doi: 10.1038/s41467-025-57594-z.
Members of the Pol A family of DNA polymerases, found across all domains of life, utilize various strategies for DNA strand separation during replication. In higher eukaryotes, mitochondrial DNA polymerase γ relies on the replicative helicase TWINKLE, whereas the yeast ortholog, Mip1, can unwind DNA independently. Using Mip1 as a model, we present a series of high-resolution cryo-EM structures that capture the process of DNA strand displacement. Our data reveal previously unidentified structural elements that facilitate the unwinding of the downstream DNA duplex. Yeast cells harboring Mip1 variants defective in strand displacement exhibit impaired oxidative phosphorylation and loss of mtDNA, corroborating the structural observations. This study provides a molecular basis for the intrinsic strand displacement activity of Mip1 and illuminates the distinct unwinding mechanisms utilized by Pol A family DNA polymerases.
DNA聚合酶A家族的成员存在于生命的所有领域，在复制过程中利用各种策略进行DNA链分离。在高等真核生物中，线粒体DNA聚合酶γ依赖于复制解旋酶TWINKLE，而酵母直系同源物Mip1可以独立解开DNA。以Mip1为模型，我们展示了一系列高分辨率冷冻电镜结构，这些结构捕捉了DNA链置换的过程。我们的数据揭示了以前未被识别的结构元件，这些元件有助于下游DNA双链的解旋。携带链置换缺陷的Mip1变体的酵母细胞表现出氧化磷酸化受损和线粒体DNA丢失，这证实了结构观察结果。这项研究为Mip1的内在链置换活性提供了分子基础，并阐明了Pol A家族DNA聚合酶所采用的不同解旋机制。
