DNA replication requires contributions from various proteins, such as DNA helicases; in mitochondria Twinkle is important for maintaining and replicating mitochondrial DNA. Twinkle helicases are predicted to also possess primase activity, as has been shown in plants; however this activity appears to have been lost in metazoans. Given this, the study of Twinkle in other organisms is required to better understand the evolution of this family and the roles it performs within mitochondria. Here we describe the characterization of a Twinkle homologue, Twm1, in the amoeba Dictyostelium discoideum, a model organism for mitochondrial genetics and disease. We show that Twm1 is important for mitochondrial function as it maintains mitochondrial DNA copy number in vivo. Twm1 is a helicase which unwinds DNA resembling open forks, although it can act upon substrates with a single 3′ overhang, albeit less efficiently. Furthermore, unlike human Twinkle, Twm1 has primase activity in vitro. Finally, using a novel in bacterio approach, we demonstrated that Twm1 promotes DNA replication. We conclude that Twm1 is a replicative mitochondrial DNA helicase which is capable of priming DNA for replication. Our results also suggest that non-metazoan Twinkle could function in the initiation of mitochondrial DNA replication. While further work is required, this study has illuminated several alternative processes of mitochondrial DNA maintenance which might also be performed by the Twinkle family of helicases.

中文翻译：

---

Twinkle（Twm1）的Dictyostelium discoideum同源物是线粒体DNA解旋酶，一种活性引发酶，可促进线粒体DNA复制。

DNA复制需要来自各种蛋白质的贡献，例如DNA解旋酶。线粒体中的闪烁对于维持和复制线粒体DNA至关重要。如植物中所示，预计闪光解旋酶也具有启动酶活性。但是，这种活动似乎在后生动物中已经消失了。鉴于此，需要对其他生物中的“闪烁”进行研究，以更好地了解该家族的进化及其在线粒体内的作用。在这里，我们描述了变形虫Dctyostelium discoideum中的闪烁同源物Twm1的特征，后者是线粒体遗传学和疾病的模型生物。我们显示Twm1对于线粒体功能很重要，因为它在体内维持线粒体DNA的拷贝数。Twm1是一种解旋酶，可展开类似于开放叉子的DNA，尽管它可以以单个3'突出端作用于底物，但效率较低。此外，与人类Twinkle不同，Twm1在体外具有启动酶活性。最后，使用一种新颖的细菌方法，我们证明了Twm1可以促进DNA复制。我们得出结论，Twm1是一种线粒体DNA解旋酶，能够引发DNA复制。我们的研究结果还表明，非metazoan闪烁可能在线粒体DNA复制的启动中起作用。尽管还需要进一步的工作，但这项研究阐明了线粒体DNA维持的几种替代过程，这些过程也可能由Twinkle家族的解旋酶完成。我们证明了Twm1促进DNA复制。我们得出结论，Twm1是一种线粒体DNA解旋酶，能够引发DNA复制。我们的研究结果还表明，非metazoan闪烁可能在线粒体DNA复制的启动中起作用。尽管还需要进一步的工作，但这项研究阐明了线粒体DNA维持的几种替代过程，这些过程也可能由Twinkle家族的解旋酶完成。我们证明了Twm1促进DNA复制。我们得出结论，Twm1是一种线粒体DNA解旋酶，能够引发DNA复制。我们的研究结果还表明，非metazoan闪烁可能在线粒体DNA复制的启动中起作用。尽管还需要进一步的工作，但这项研究阐明了线粒体DNA维持的几种替代过程，这些过程也可能由Twinkle家族的解旋酶完成。