Plant and Microbial Biology, University of California - Berkeley, Berkeley, CA 94720, USA.
Nucleic Acids Res. 2024 Sep 23;52(17):10431-10446. doi: 10.1093/nar/gkae675.
ICP1, a lytic bacteriophage of Vibrio cholerae, is parasitized by phage satellites, PLEs, which hijack ICP1 proteins for their own horizontal spread. PLEs' dependence on ICP1's DNA replication machinery and virion components results in inhibition of ICP1's lifecycle. PLEs are expected to depend on ICP1 factors for genome packaging, but the mechanism(s) PLEs use to inhibit ICP1 genome packaging is currently unknown. Here, we identify and characterize Gpi, PLE's indiscriminate genome packaging inhibitor. Gpi binds to ICP1's large terminase (TerL), the packaging motor, and blocks genome packaging. To overcome Gpi's negative effect on TerL, a component PLE also requires, PLE uses two genome packaging specifiers, GpsA and GpsB, that specifically allow packaging of PLE genomes. Surprisingly, PLE also uses mimicry of ICP1's pac site as a backup strategy to ensure genome packaging. PLE's pac site mimicry, however, is only sufficient if PLE can inhibit ICP1 at other stages of its lifecycle, suggesting an advantage to maintaining Gpi, GpsA and GpsB. Collectively, these results provide mechanistic insights into another stage of ICP1's lifecycle that is inhibited by PLE, which is currently the most inhibitory of the documented phage satellites. More broadly, Gpi represents the first satellite-encoded inhibitor of a phage TerL.
肠凝聚性噬菌体 1（ICP1）是霍乱弧菌的一种裂解性噬菌体，它被噬菌体卫星 PLE 寄生，后者劫持 ICP1 蛋白以实现自身的水平传播。PLE 对 ICP1 的 DNA 复制机制和病毒粒子成分的依赖导致 ICP1 生命周期受到抑制。预计 PLE 将依赖 ICP1 因子进行基因组包装，但 PLE 抑制 ICP1 基因组包装的机制目前尚不清楚。在这里，我们鉴定并表征了 PLE 的非特异性基因组包装抑制剂 Gpi。Gpi 结合 ICP1 的大型末端酶（TerL），即包装马达，从而阻止基因组包装。为了克服 Gpi 对 TerL 的负面影响，PLE 还需要一个组件，即 PLE 使用两种基因组包装指定蛋白 GpsA 和 GpsB，专门允许 PLE 基因组的包装。令人惊讶的是，PLE 还使用 ICP1 的 pac 位点模拟作为后备策略来确保基因组包装。然而，只有在 PLE 能够抑制 ICP1 生命周期的其他阶段时，PLE 的 pac 位点模拟才足够，这表明维持 Gpi、GpsA 和 GpsB 具有优势。总的来说，这些结果为 ICP1 生命周期的另一个阶段提供了机制上的见解，该阶段受到 PLE 的抑制，而 PLE 是目前已记录的噬菌体卫星中抑制作用最强的。更广泛地说，Gpi 代表了第一个由卫星编码的噬菌体 TerL 抑制剂。
