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An essential and highly selective protein import pathway encoded by nucleus-forming phage. | LitMetric

AI Article Synopsis

  • The Chimalliviridae phages have a unique structure called a phage nucleus, made of the protein chimallin, which separates transcription and translation while allowing selective protein import.* -
  • Researchers identified two key components in the protein import process: a phage surface protein necessary for nuclear entry and a conserved protein named PicA that helps transport proteins across the nuclear membrane.* -
  • The study proposes a model for the "Protein Import Chimallivirus" (PIC) pathway, suggesting that proteins are guided by their surface amino acids to PicA, which then allows them entry into the phage nucleus, highlighting its role in the evolutionary battle between phages and their bacterial hosts.*

Article Abstract

Unlabelled: Targeting proteins to specific subcellular destinations is essential in prokaryotes, eukaryotes, and the viruses that infect them. Chimalliviridae phages encapsulate their genomes in a nucleus-like replication compartment composed of the protein chimallin (ChmA) that excludes ribosomes and decouples transcription from translation. These phages selectively partition proteins between the phage nucleus and the bacterial cytoplasm. Currently, the genes and signals that govern selective protein import into the phage nucleus are unknown. Here we identify two components of this novel protein import pathway: a species-specific surface-exposed region of a phage intranuclear protein required for nuclear entry and a conserved protein, PicA, that facilitates cargo protein trafficking across the phage nuclear shell. We also identify a defective cargo protein that is targeted to PicA on the nuclear periphery but fails to enter the nucleus, providing insight into the mechanism of nuclear protein trafficking. Using CRISPRi-ART protein expression knockdown of PicA, we show that PicA is essential early in the chimallivirus replication cycle. Together our results allow us to propose a multistep model for the Protein Import Chimallivirus (PIC) pathway, where proteins are targeted to PicA by amino acids on their surface, and then licensed by PicA for nuclear entry. The divergence in the selectivity of this pathway between closely-related chimalliviruses implicates its role as a key player in the evolutionary arms race between competing phages and their hosts.

Significance Statement: The phage nucleus is an enclosed replication compartment built by Chimalliviridae phages that, similar to the eukaryotic nucleus, separates transcription from translation and selectively imports certain proteins. This allows the phage to concentrate proteins required for DNA replication and transcription while excluding DNA-targeting host defense proteins. However, the mechanism of selective trafficking into the phage nucleus is currently unknown. Here we determine the region of a phage nuclear protein that targets it for nuclear import and identify a conserved, essential nuclear shell-associated protein that plays a key role in this process. This work provides the first mechanistic model of selective import into the phage nucleus.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC10983916PMC
http://dx.doi.org/10.1101/2024.03.21.585822DOI Listing

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