Satellite phage P4 molecular piracy of helper myovirus P2 morphogenetic, packaging, and lysis machinery

A cross-genome molecular piracy module in which satellite bacteriophage P4 (Enterobacteria phage P4, 11.6 kb, lacking genes for structural capsid, tail, terminase, or lysis proteins) hijacks the morphogenetic, DNA-packaging, and host-lysis apparatus of a coinfecting or lysogenic Peduoviridae helper phage such as Escherichia phage P2 (33.5 kb). The piracy program operates across four tightly coupled stages: (1) Helper prophage derepression, in which P4 derepression protein Epsilon binds the P2 immunity repressor C to prevent operator binding and induce P2 prophage excision and lytic gene expression, while P4 replicates its own 11.6-kb genome autonomously via its bifunctional primase-helicase-origin-binding protein Alpha; (2) Cross-genome late transcriptional transactivation and antitermination, in which the P4 tandem-Ogr-domain zinc-finger protein Delta (paralleling P2's own late activator Ogr) binds the alpha-CTD of host Escherichia coli RNA polymerase to activate P2's four morphogenetic and lysis promoters (PP, PO, PV, PJ), while P4 polarity suppression protein Psu binds and hyper-oligomerizes host transcription termination factor Rho to prevent premature termination across the hijacked P2 late operons; (3) Capsid size redirection, in which P4 protein Sid polymerizes into an external dodecahedral cage around assembling P2 gpN major capsid hexamers and gpO internal protease/scaffold subunits, redirecting procapsid geometry from the helper's T=7 head (60 nm, 35-kb capacity) to a threefold smaller T=4 head (45 nm, 11.6-kb capacity) that physically excludes the full-length P2 helper genome; and (4) Cos-site packaging piracy, in which P4 carries an identical 19-bp 5'-cohesive cos site recognized by the P2 terminase complex (small endonuclease subunit gpM and large ATPase subunit gpP), packaging the 11.6-kb P4 genome through the P2 gpQ portal into the Sid-constricted T=4 capsid before P2 tail attachment and lysis.

Exemplar satellite-helper pair: Enterobacteria phage P4 (NCBITaxon:10680) and Bacteriophage P2 (NCBITaxon:2905681). Generalizes across P4-like phage satellites (e.g. Retron-harboring P4 satellites, Phage Inducible Chromosomal Islands / PICIs such as Staphylococcus aureus SaPIs, and ICP1-associated PLEs) that combine helper derepression, late promoter transactivation, external or internal scaffold-mediated capsid remodeling (T=7 to T=4), and packaging site mimicry.