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The T7 pore complex, gp14/gp15/gp16 (Hu et al. 2013). Many tailed bacteriophages assemble ejection proteins and a portal-tail complex at a unique vertex of the capsid. The ejection proteins form a transenvelope channel extending the portal-tail channel for the delivery of genomic DNA in cell infection. Chen et al. 2021 reported the structure of the mature bacteriophage T7, including the ejection proteins, as well as the structures of the full and empty T7 particles in complex with their cell receptor lipopolysaccharide. The near-atomic-resolution reconstruction showed that the ejection proteins in the mature T7 assemble into a core, which comprises a fourfold gene product 16 (gp16) ring, an eightfold gp15 ring, and a putative eightfold gp14 ring. The gp15 and gp16 are mainly composed of helix bundles, and gp16, with two 3 TMS bundles at residues 310 - 420 and 1130 - 1270, respectively, harbors a lytic transglycosylase domain for degrading the bacterial peptidoglycan layer. When interacting with the lipopolysaccharide, the T7 tail nozzle opens. Six copies of gp14 anchor to the tail nozzle, extending the nozzle across the lipopolysaccharide lipid bilayer. The structures of gp15 and gp16 in the mature T7 suggest that they should undergo remarkable conformational changes to form the transenvelope channel. Hydrophobic α-helices were observed in gp16 but not in gp15, suggesting that gp15 forms the channel in the hydrophilic periplasm and gp16 forms the channel in the cytoplasmic membrane (Chen et al. 2021).

The T7 pore complex formed from internal virion protein gp14/gp15/gp16 gp14 (internal virion protein B) (P03724) (196 aas)
gp15 (internal virion protein C) (P03725) (747 aas)
gp16 (internal virion protein D) (P03726) (1318 aas)   plus
The HsdR subunit of the EcoK1 restriction/modification enzyme of E. coli (P08956)

Cytosine specific methyltransferase of 227 aa

Methyltransferase of Siphoviridae sp.