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G3P (pIII) mediates initial phage adsorption to the tip of the host F-pilus, triggering pilus retraction toward the host inner membrane.
"During the initial step of infection, G3P mediates adsorption of the phage to its primary receptor, the tip of host F-pilus. Attachment of the phage causes pilus retraction bringing the viral particle into close proximity of the host cell inner membrane."
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F-pilus binding induces a conformational change in G3P that enables interaction with the host TolA, TolQ, and TolR entry receptors, while the C-terminal domain mediates virion release during extrusion.
"Binding to the host pilus initiates a change in the G3P conformation, allowing subsequent interaction with the host entry receptors TolA, TolQ and TolR and penetration of the viral DNA into the host cytoplasm. In the extrusion process, G3P mediates the release of the membrane-anchored virion from the cell via its C-terminal domain."
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G3P resides in the bacterial host inner membrane prior to assembly and is present in five copies at the head (proximal) tip of the mature virion.
"Prior to assembly, G3P is found associated with the bacterial host inner membrane. There are about five copies of this protein per mature phage that are located on the head side of the filamentous virion."