To efficiently replicate, phages must avoid bacterial defence systems that target nucleic acids. Two studies report that a nucleus-like structure protects jumbo phages against DNA-targeting immune pathways. Bondy-Denomy and colleagues showed that jumbo phage ϕKZ, which infects Pseudomonas aeruginosa, is resistant to CRISPR systems that are found in its natural host (types I-C and I-F), to those that are not naturally present in P. aeruginosa species (types II-A and V-A) and to restriction endonucleases (types I and II). Phage ϕKZ assembles a proteinaceous compartment in which phage DNA replication occurs, which led the authors to hypothesize that this structure provides a physical protective barrier against DNA-targeting enzymes. Indeed, Cas proteins and restriction enzymes were excluded from the structure, whereas targeting the type II restriction enzyme EcoRI inside the compartment decreased phage titres and protected host cells. Finally, the authors showed that phage ϕKZ is susceptible to Cas13a, which targets RNA, possibly as mRNA is exported into the cytoplasm for translation. Fineran and colleagues report that a Serratia jumbo phage, PCH45, which is distinct from other described jumbo phages such as Pseudomonas phages, evades type I CRISPR–Cas systems independently of DNA modification or anti-CRISPR. By contrast, the type III-A system provided phage resistance by targeting phage RNA in the cytoplasm. As the Serratia jumbo phage encodes a tubulin homologue and a potential shell protein, the authors also investigated the possibility that the phages produce a protective nucleus-like compartment. They showed that shell proteins assembled into a spherical structure enclosing the phage DNA upon infection and that native CRISPR–Cas complexes in Serratia (types I-E, I-F and III-A) were excluded from this compartment. In sum, the studies suggest that the formation of a nucleus-like structure in the bacterial cytoplasm may be a widespread defence strategy against DNA-targeting immune pathways among jumbo phages.