Multi-interface licensing of protein import into a phage nucleus

Area of Science:

• Microbiology
• Molecular Biology
• Virology

Background:

• Bacteriophages, particularly jumbo phages like ΦKZ, evade host defenses by forming a nucleus-like compartment.
• This compartment sequesters phage DNA replication and transcription machinery, excluding host nucleases.
• The specific phage proteins and mechanisms governing import into this compartment are largely unknown.

Purpose of the Study:

• To identify and characterize the phage factors responsible for protein import into the nucleus-like compartment of ΦKZ-like jumbo phages.
• To elucidate the mechanisms of selectivity employed by these phages to regulate cargo entry.
• To understand the roles of conserved and non-conserved phage proteins in this import process.

Main Methods:

• Utilized a genetic selection strategy to identify phage mutants with altered protein import capabilities.
• Investigated protein-protein interactions using co-localization and interaction studies.
• Characterized the function of specific import factors (Imp1, Imp3, Imp6, Imp2, Imp4/Imp5) in the context of nuclear localization of phage proteins and host topoisomerase.

Main Results:

• Discovered a conserved core import system involving Imp1, Imp3, and Imp6.
• Demonstrated that Imp1 possesses multiple interfaces, each mediating the import of distinct nuclear-localized phage proteins.
• Identified Imp3 as crucial for Imp1 function and Imp2, Imp4/Imp5 as potential cargo-specific adaptors for certain proteins.

Conclusions:

• Proposed a model for a core protein import system in nucleus-forming phages, centered around Imp1, Imp3, and Imp6.
• Highlighted the adaptability of the Imp1 factor, utilizing different interfaces for diverse cargo.
• Suggests a sophisticated mechanism for regulating protein traffic within the phage-derived nuclear compartment.