phage nucleus

cellstructuremech:phage_nucleus · Other · Protein shelled organelle · Proposed

A jumbo-bacteriophage protein-shelled compartment that assembles in infected bacterial cells, surrounds replicating phage DNA, and spatially separates phage genome replication and transcription from bacterial translation. [DOI:10.1126/science.aal2130]

Synonyms: phage nuclear shell; jumbo bacteriophage nuclear shell; nucleus-like compartment

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
chimallin	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	chmA, gp105		ESSENTIAL	Major phage nuclear shell protein that polymerizes into the proteinaceous lattice surrounding replicating jumbo-phage DNA. `DOI:10.1126/science.aal2130` Chaikeeratisak et al. 2017 identified 201phi2-1 gp105 as an early, highly expressed phage protein that forms the nucleus-like shell. `DOI:10.1038/s41586-022-05013-4` Laughlin et al. 2022 named the major jumbo-bacteriophage nuclear shell protein chimallin and analyzed its shell self-assembly.

Taxonomic distribution

NCBITaxon:198110 Pseudomonas phage 201phi2-1 — COMMON: Pseudomonas phage 201phi2-1 forms a chimallin-lined phage nucleus during infection of Pseudomonas chlororaphis. [DOI:10.1126/science.aal2130]

Canonical examples

NCBITaxon:198110 Pseudomonas phage 201phi2-1 — Jumbo phage whose gp105 shell established the nucleus-like compartment in infected Pseudomonas chlororaphis cells. [DOI:10.1126/science.aal2130]

Functions

phage genome compartmentalization — The phage nucleus shell encloses replicating phage DNA and separates viral replication and transcription from ribosomal translation in the infected bacterial cytoplasm.
- DOI:10.1126/science.aal2130 Chaikeeratisak et al. 2017 found that gp105 shells surround phage DNA while excluding ribosomes.
- DOI:10.1016/j.celrep.2017.07.064 Chaikeeratisak et al. 2017 showed that nucleus-like compartments and PhuZ spindles are conserved among large Pseudomonas phages.
phage DNA antidefense shielding — The chimallin shell blocks access of some bacterial DNA-targeting immune machineries to the phage genome.
- DOI:10.1038/s41564-019-0612-5 Malone et al. 2020 showed that a phage nucleus protects jumbo-phage DNA from CRISPR-Cas DNA targeting while remaining vulnerable to type III RNA-targeting immunity.
- DOI:10.1038/s41586-022-05013-4 Laughlin et al. 2022 linked chimallin shell architecture with selective exchange across the jumbo-phage nuclear shell.

Mechanism graphs

Chimallin shells enclose jumbo-phage DNA (ASSEMBLY)

Chimallin polymerizes into a phage nuclear shell that encloses replicating phage DNA in a proteinaceous nucleus-like compartment.

Subject	Predicate	Object	Evidence
chimallin	self-assembles into	phage nucleus	`DOI:10.1126/science.aal2130` Chaikeeratisak et al. 2017 localized 201phi2-1 gp105 to the phage nucleus-like shell. `DOI:10.1038/s41586-022-05013-4` Laughlin et al. 2022 resolved chimallin shell architecture and self-assembly.
phage nucleus	encloses	replicating phage DNA	`DOI:10.1126/science.aal2130` Chaikeeratisak et al. 2017 observed the 201phi2-1 nucleus-like shell surrounding phage DNA.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral grounding for chimallin major phage nuclear shell proteins. This first record leaves chimallin ungrounded rather than asserting that a broad phage-shell accession, an unverified chimallin-like cluster or a virus-specific gp105 accession is equivalent to the jumbo-phage nuclear shell family.
INTERPRETATION (RESOLVED): PhuZ is not asserted as a phage nucleus shell constituent. PhuZ forms a tubulin-like spindle that positions and rotates the phage nucleus, but the first phage-nucleus record models the chimallin shell rather than the separate spindle polymer.

Evidence

DOI:10.1126/science.aal2130 Chaikeeratisak et al. 2017, 'Assembly of a nucleus-like structure during viral replication in bacteria', Science.
DOI:10.1016/j.celrep.2017.07.064 Chaikeeratisak et al. 2017, 'The Phage Nucleus and Tubulin Spindle Are Conserved among Large Pseudomonas Phages', Cell Reports.
DOI:10.1038/s41564-019-0612-5 Malone et al. 2020, 'A jumbo phage that forms a nucleus-like structure evades CRISPR-Cas DNA targeting but is vulnerable to type III RNA-based immunity', Nature Microbiology.
DOI:10.1038/s41586-022-05013-4 Laughlin et al. 2022, 'Architecture and self-assembly of the jumbo bacteriophage nuclear shell', Nature.

Curation history

2026-09-11T12:24:09Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-11T12:25:01Z codex · EXPANDED_RECORD — Added non-membrane-bounded-organelle parentage, phage nucleus synonymy, chimallin shell curation, 201phi2-1 scope, compartmentalization and antidefense functions, DOI evidence, a nonmechanistic chimallin assembly graph, and chimallin grounding and PhuZ boundary discussions.
2026-09-11T12:31:24Z codex · REVIEW_FIX — Addressed PR review issue #479 by narrowing the chimallin grounding TODO rationale so it no longer suggests an unsupported HK97-like fold equivalence.

Source: data/structures/other/phage_nucleus.yaml