| Claim/annotation | Supporting evidence (short quote/paraphrase) | Quantitative data | Source (with year, journal, URL) |
|---|---|---|---|
| Verified identity and location | T4 gp54 is annotated as a baseplate/tail structural protein located at the “Baseplate-tail tube junction”; this matches UniProt P13341 description as a baseplate tail-tube junction protein. (pqac-00000002, pqac-00000004, pqac-00000005) | Monomer mass ~35.0 kDa; 6 copies per tail; oligomeric state ND | Leiman et al., Dec 2010, *Virology Journal*, https://doi.org/10.1186/1743-422x-7-355 ; Rossmann et al., Apr 2004, *Current Opinion in Structural Biology*, https://doi.org/10.1016/j.sbi.2004.02.001 |
| Baseplate component added late in assembly | Baseplate assembly is “completed” by attachment of six copies each of gp48 and gp54 at the external interface between wedges and the hub. (pqac-00000001, pqac-00000003, pqac-00000006, pqac-00000008) | 6 copies gp54 + 6 copies gp48 | Kostyuchenko et al., Sep 2003, *Nature Structural Biology*, https://doi.org/10.1038/nsb970 ; Leiman et al., Nov 2003, *Cellular and Molecular Life Sciences*, https://doi.org/10.1007/s00018-003-3072-1 ; Arisaka et al., Nov 2016, *Biophysical Reviews*, https://doi.org/10.1007/s12551-016-0230-x |
| Primary function: initiator/platform for tail tube assembly | gp48 and gp54 “create a platform on top of the hub” or “serve as a starting point” that initiates oligomerization/polymerization of gp19 into the tail tube. (pqac-00000000, pqac-00000003, pqac-00000005, pqac-00000009, pqac-00000010) | Tail tube built from gp19; reported as 138 copies in one review and 144 copies in another review of assembled tails/baseplate context | Rossmann et al., Apr 2004, *Current Opinion in Structural Biology*, https://doi.org/10.1016/j.sbi.2004.02.001 ; Leiman et al., Nov 2003, *Cellular and Molecular Life Sciences*, https://doi.org/10.1007/s00018-003-3072-1 ; Yap et al., Feb 2016, *PNAS*, https://doi.org/10.1073/pnas.1601654113 |
| Role in initiating sheath assembly indirectly through junction complex | gp48/gp54 are required to initiate assembly of both the tail tube and the contractile sheath; gp25 binds the gp48–gp54 complex and likely helps start sheath polymerization. (pqac-00000001, pqac-00000009) | gp25 fitted as interacting with gp48–gp54 complex; sheath/tube each reported with 138 or 144 subunits depending on source | Kostyuchenko et al., Sep 2003, *Nature Structural Biology*, https://doi.org/10.1038/nsb970 ; Yap et al., Feb 2016, *PNAS*, https://doi.org/10.1073/pnas.1601654113 |
| Interaction partners supported by assembly/structure studies | Named partners include gp48 (co-platform protein), gp19 (tail tube protein polymerized from gp54 platform), gp29/tape measure protein (associated with tube initiation), and gp25 (binds gp48–gp54 complex before sheath assembly). (pqac-00000008, pqac-00000009, pqac-00000010) | gp54 is ~320 aa in one structural review; gp19 forms 23 hexameric rings = 138 copies in one model | Arisaka et al., Nov 2016, *Biophysical Reviews*, https://doi.org/10.1007/s12551-016-0230-x ; Yap et al., Feb 2016, *PNAS*, https://doi.org/10.1073/pnas.1601654113 ; Leiman et al., Nov 2003, *Cellular and Molecular Life Sciences*, https://doi.org/10.1007/s00018-003-3072-1 |
| Structural placement in cryo-EM maps | In a 12 Å cryo-EM reconstruction of the baseplate/tail-tube complex, density at the top/outside of the dome where the tail tube joins the baseplate was assigned as gp54 or gp48; later higher-resolution work resolved previously unsolved proteins including gp48/gp54. (pqac-00000000, pqac-00000001, pqac-00000008) | 12 Å cryo-EM map (2003/2004-era assignment); 3.8 Å cryo-EM cited for later in vitro assembled complexes | Kostyuchenko et al., Sep 2003, *Nature Structural Biology*, https://doi.org/10.1038/nsb970 ; Rossmann et al., Apr 2004, *Current Opinion in Structural Biology*, https://doi.org/10.1016/j.sbi.2004.02.001 ; Arisaka et al., Nov 2016, *Biophysical Reviews*, https://doi.org/10.1007/s12551-016-0230-x |
| Stoichiometry and virion localization are consistent across reviews | Multiple reviews independently list gp54 as a 6-copy structural protein at the baseplate/baseplate–tail tube junction, assembled before gp19 tube and gp18 sheath. (pqac-00000002, pqac-00000003, pqac-00000011) | 6 copies per tail; ~35.0 kDa; ordered before gp19 and gp18 in assembly tables | Leiman et al., Dec 2010, *Virology Journal*, https://doi.org/10.1186/1743-422x-7-355 ; Leiman et al., Nov 2003, *Cellular and Molecular Life Sciences*, https://doi.org/10.1007/s00018-003-3072-1 |
| Evolutionary/structural inference | gp54 is predicted to contain a domain with a fold similar to the tail-tube protein, supporting its role as a tube initiator/adaptor rather than an enzyme. (pqac-00000009) | Fold similarity inferred; no enzyme activity reported | Yap et al., Feb 2016, *PNAS*, https://doi.org/10.1073/pnas.1601654113 |
| Evidence type and limitations | Evidence is strong for structural role, location, stoichiometry, and assembly order, but direct gp54-specific mutant phenotypes and solved standalone atomic structure/domain family assignments were not provided in the cited context. (pqac-00000001, pqac-00000011) | Oligomeric state ND; no PDB listed for gp54 in review tables | Kostyuchenko et al., Sep 2003, *Nature Structural Biology*, https://doi.org/10.1038/nsb970 ; Leiman et al., Dec 2010, *Virology Journal*, https://doi.org/10.1186/1743-422x-7-355 |


*Table: This table summarizes the main functional annotation evidence for bacteriophage T4 gp54 (UniProt P13341), focusing on location, stoichiometry, assembly role, interaction partners, and structural support. It is useful as a compact evidence map for the final research report.*