Argonaute proteins use single-stranded RNA or DNA guides to target complementary nucleic acids. This allows eukaryotic Argonaute proteins to mediate RNA interference and long prokaryotic Argonaute proteins to interfere with invading nucleic acids. The function and mechanisms of the phylogenetically distinct short prokaryotic Argonaute proteins remain poorly understood. We demonstrate that short prokaryotic Argonaute and the associated TIR-APAZ (SPARTA) proteins form heterodimeric complexes. Upon guide RNA-mediated target DNA binding, four SPARTA heterodimers form oligomers in which TIR domain-mediated NAD(P)ase activity is unleashed. When expressed in Escherichia coli, SPARTA is activated in the presence of highly transcribed multicopy plasmid DNA, which causes cell death through NAD(P)⁺ depletion. This results in the removal of plasmid-invaded cells from bacterial cultures. Furthermore, we show that SPARTA can be repurposed for the programmable detection of DNA sequences. In conclusion, our work identifies SPARTA as a prokaryotic immune system that reduces cell viability upon RNA-guided detection of invading DNA.

Argonaute 蛋白使用单链 RNA 或 DNA 引导来靶向互补核酸。这使得真核 Argonaute 蛋白能够介导 RNA 干扰，而长原核 Argonaute 蛋白能够干扰入侵的核酸。系统发育上不同的短原核 Argonaute 蛋白的功能和机制仍然知之甚少。我们证明短原核 Argonaute 和相关的 TIR-APAZ (SPARTA) 蛋白形成异二聚体复合物。在引导 RNA 介导的靶 DNA 结合后，四个 SPARTA 异二聚体形成寡聚体，其中 TIR 结构域介导的 NAD(P)ase 活性被释放。当在大肠杆菌中表达时，SPARTA 在高度转录的多拷贝质粒 DNA 存在下被激活，通过 NAD(P) ⁺耗尽导致细胞死亡。这导致从细菌培养物中去除质粒侵入的细胞。此外，我们还表明 SPARTA 可以重新用于 DNA 序列的可编程检测。总之，我们的工作将 SPARTA 确定为一种原核免疫系统，可在 RNA 引导检测入侵 DNA 时降低细胞活力。