Bacteriophages are the most abundant biological entities on Earth, but our understanding of many aspects of their lifecycles is still incomplete. Here, we have structurally analysed the infection cycle of the siphophage Casadabanvirus JBD30. Using its baseplate, JBD30 attaches to Pseudomonas aeruginosa via the bacterial type IV pilus, whose subsequent retraction brings the phage to the bacterial cell surface. Cryo-electron microscopy structures of the baseplate-pilus complex show that the tripod of baseplate receptor-binding proteins attaches to the outer bacterial membrane. The tripod and baseplate then open to release three copies of the tape-measure protein, an event that is followed by DNA ejection. JBD30 major capsid proteins assemble into procapsids, which expand by 7% in diameter upon filling with phage dsDNA. The DNA-filled heads are finally joined with 180-nm-long tails, which bend easily because flexible loops mediate contacts between the successive discs of major tail proteins. It is likely that the structural features and replication mechanisms described here are conserved among siphophages that utilize the type IV pili for initial cell attachment.

中文翻译：

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铜绿假单胞菌噬菌体 JBD30 的结构和复制。


噬菌体是地球上最丰富的生物实体，但我们对其生命周期的许多方面的了解仍然不完整。在这里，我们对 siphophage Casadabanvirus JBD30 的感染周期进行了结构分析。JBD30 利用其底板，通过细菌 IV 型菌毛附着在铜绿假单胞菌上，随后菌毛的回缩将噬菌体带到细菌细胞表面。底板-菌毛复合体的冷冻电子显微镜结构显示，底板受体结合蛋白的三脚架附着在细菌外膜上。然后打开三脚架和底板以释放三个卷尺蛋白拷贝，这一事件随后是 DNA 喷射。JBD30 主要衣壳蛋白组装成前衣壳，前衣壳在填充噬菌体 dsDNA 后直径膨胀 7%。充满 DNA 的头部最终与 180 nm 长的尾部连接，这些尾部很容易弯曲，因为柔性环介导了主要尾蛋白的连续圆盘之间的接触。此处描述的结构特征和复制机制很可能在利用 IV 型菌毛进行初始细胞附着的 siphophages 中是保守的。