In many eukaryotes, Argonaute proteins, guided by short RNA sequences, defend cells against transposons and viruses. In the eubacterium Thermus thermophilus, the DNA-guided Argonaute TtAgo defends against transformation by DNA plasmids. Here, we report that TtAgo also participates in DNA replication. In vivo, TtAgo binds 15- to 18-nt DNA guides derived from the chromosomal region where replication terminates and associates with proteins known to act in DNA replication. When gyrase, the sole T. thermophilus type II topoisomerase, is inhibited, TtAgo allows the bacterium to finish replicating its circular genome. In contrast, loss of gyrase and TtAgo activity slows growth and produces long sausage-like filaments in which the individual bacteria are linked by DNA. Finally, wild-type T. thermophilus outcompetes an otherwise isogenic strain lacking TtAgo. We propose that the primary role of TtAgo is to help T. thermophilus disentangle the catenated circular chromosomes generated by DNA replication.

在许多真核生物中，Argonaute 蛋白在短 RNA 序列的引导下，保护细胞免受转座子和病毒的侵害。在嗜热栖热菌真细菌中，DNA 引导的 Argonaute TtAgo 可防御 DNA 质粒的转化。在这里，我们报告 TtAgo 也参与 DNA 复制。在体内，TtAgo 结合来自复制终止的染色体区域的 15 至 18 nt DNA 引导分子，并与已知在 DNA 复制中起作用的蛋白质结合。当旋转酶（唯一的嗜热嗜热菌II 型拓扑异构酶）受到抑制时，TtAgo 允许细菌完成其环状基因组的复制。相比之下，旋转酶和 TtAgo 活性的丧失会减慢生长速度，并产生香肠状的长丝，其中各个细菌通过 DNA 连接起来。最后，野生型嗜热嗜热菌战胜了缺乏 TtAgo 的其他同基因菌株。我们认为 TtAgo 的主要作用是帮助嗜热嗜热菌解开 DNA 复制产生的连锁环状染色体。