Defining the constituents and functions of a lipid-based jumbo phage compartment

Abstract

Viruses are vulnerable to cellular defenses at the start of the infection when a single copy genome has not yet initiated de novo viral protein synthesis. A family of jumbo phages related to phage {Phi}KZ, which infects Pseudomonas aeruginosa, uses a protein-based phage nucleus to protect the DNA during middle and late stages of infection, but how it is protected prior to phage nucleus assembly is unclear. To reveal the environment surrounding injected phage DNA, we determine which proteins interact with phage proteins injected with the phage genome. Here, we surprisingly identify host proteins related to membrane and lipid biology co-purifying with the injected phage protein. Staining of infected cells with lipophilic dyes revealed a clustering of host lipids co-localized with phage DNA and protein in an early phage infection (EPI) vesicle. Early gene expression is induced by the co-injected virion RNAP (vRNAP), with specific early proteins then associating with the EPI vesicle and ribosomes, likely to facilitate localized translation. As the infection progresses, the phage genome separates from the EPI vesicle and vRNAP, moving into the nascent proteinaceous phage nucleus. Enzymes involved in DNA replication and CRISPR/restriction immune nucleases notably do not localize to the EPI vesicle, supporting that DNA is not exposed at this early time point. We therefore propose that the EPI vesicle is rapidly constructed together with injected phage proteins, phage DNA, host lipids, and host membrane proteins to enable genome protection, early transcription, localized translation, and to ensure the faithful transfer of the single copy phage genome to the proteinaceous nucleus.