| Claim/Function | Evidence type | Key quantitative details | Interaction partners | Primary citation |
|---|---|---|---|---|
| T4 gp25 is a small baseplate wedge component in the assembled tail; part of the gp6-gp25-gp53 assembly unit and incorporated late during wedge formation. | Review/compilation integrating biochemical and cryo-EM mapping | 15.1 kDa; 6 copies per virion/baseplate; baseplate/tail tube reconstructed at ~12 Å. | gp6, gp53; wedge proteins overall include gp11, gp10, gp7, gp8, gp6, gp53, gp25. | Rossmann et al., 2004, DOI: https://doi.org/10.1016/j.sbi.2004.02.001 (pqac-00000005) |
| gp25 contributes to an unassigned platform on top of the T4 baseplate that resembles a sheath layer and likely helps connect baseplate to tail sheath/tube. | Cryo-EM fitting / density assignment | Cryo-EM baseplate resolution 12 Å; gp25 reported as 5.1 kDa and 6 copies per baseplate; unassigned wedge-center density ~166 kDa per wedge. | Associated in unresolved density with gp6 and gp53. | Mesyanzhinov et al., 2004, DOI: https://doi.org/10.1007/pl00021751 (pqac-00000001) |
| gp25 localizes inside the gp6 ring within each wedge and helps form the platform on which the first disk of sheath protein gp18 assembles. | Cryo-EM fitting with volumetric calibration | gp25 length 142 residues; dome/star maps at ~12 Å and ~17 Å; blob volumes calibrated to assign gp25/gp53 after fitting gp6 crystal structure. | gp6, gp53, gp18; platform also linked with gp48. | Aksyuk et al., 2009, DOI: https://doi.org/10.1016/j.str.2009.04.005 (pqac-00000003) |
| gp25 strengthens both interwedge and hub-wedge connections and is positioned at the sheath initiation interface; structural fitting supports a role in baseplate attachment and sheath polymerization. | Pseudo-atomic model / structural assembly study | gp25 crystal structure referenced as PDB 4HRZ; figure evidence shows gp25 x6 at sheath initiation interface on top of hub. | gp53, gp6, gp48-gp54 complex. | Yap et al., 2016, DOI: https://doi.org/10.1073/pnas.1601654113 (pqac-00000000, pqac-00000010) |
| gp25 acts as the initiator/nucleus for tail sheath polymerization in the extended T4 tail; it continues the sheath lattice and accommodates arms from the first sheath ring. | Pseudo-atomic model of intact tail/baseplate | 6 gp25 molecules accommodate 12 long sheath arms; gp25 crystal PDB 4HRZ; baseplate model published in Nature 2016. | Tail sheath gp18; nearby hub/tube proteins gp29 and gp48. | Taylor et al., 2016, DOI: https://doi.org/10.1038/nature17971 (pqac-00000002) |
| gp25 is functionally annotated as the T4 baseplate “sheath initiator” in a synthesis of tail assembly and structure. | Review/compilation | 132 aa; stoichiometry 6 copies; structural entry PDB 5IW9; related high-resolution baseplate cryo-EM reported at 3.8 Å. | Contextual wedge/baseplate assembly with gp10, gp7, gp8, gp6, gp53, gp11; sheath polymerization by gp18. | Arisaka et al., 2016, DOI: https://doi.org/10.1007/s12551-016-0230-x (pqac-00000004) |
| In Vibrio phage XM1, gp15 is a homolog of T4 gp25 and is explicitly assigned as the sheath initiator that binds the baseplate before the first sheath ring assembles, supporting conservation of gp25-like function. | Homolog study / near-atomic cryo-EM | Distal tail/baseplate reconstructed at 3.2 Å; contracted-particle map 9.1 Å; one gp15 per wedge in atomic model. | gp11, wedge proteins, sheath protein gp6. | Wang et al., 2023, DOI: https://doi.org/10.3390/v15081673 (pqac-00000008) |


*Table: This table summarizes the main experimental and comparative evidence used to functionally annotate bacteriophage T4 gp25 (UniProt P09425). It highlights how structural fitting, pseudo-atomic models, and homolog studies converge on a role for gp25 as a baseplate wedge protein and sheath assembly initiator.*