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：

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Twinkle 的盘基网柄菌同源物 Twm1 是一种线粒体 DNA 解旋酶，一种活性引物酶，可促进线粒体 DNA 复制。


DNA 复制需要各种蛋白质的贡献，例如 DNA 解旋酶；在线粒体中，Twinkle 对于维持和复制线粒体 DNA 非常重要。正如在植物中所显示的那样，预计 Twinkle 解旋酶也具有引物酶活性；然而，这种活性似乎在后生动物中消失了。鉴于此，需要在其他生物体中研究 Twinkle，以更好地了解该家族的进化及其在线粒体中发挥的作用。在这里，我们描述了盘基网柄菌变形虫中 Twinkle 同源物 Twm1 的特征，盘基网柄菌是一种线粒体遗传学和疾病的模型生物。我们证明 Twm1 对于线粒体功能很重要，因为它在体内维持线粒体 DNA 拷贝数。 Twm1 是一种解旋酶，可以像开放叉一样解开 DNA，但它可以作用于具有单个 3' 突出端的底物，尽管效率较低。此外，与人类 Twinkle 不同，Twm1 在体外具有引物酶活性。最后，使用一种新颖的细菌方法，我们证明了 Twm1 促进 DNA 复制。我们得出结论，Twm1 是一种复制性线粒体 DNA 解旋酶，能够启动 DNA 复制。我们的结果还表明，非后生动物 Twinkle 可以在线粒体 DNA 复制的启动中发挥作用。虽然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 解旋酶家族执行。