P39504

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Comprehensive research report: bacteriophage T4 y13K (UniProt P39504) — i‑spanin (pseT.3)

0) Identity verification (critical disambiguation)

The target protein UniProt P39504 is correctly matched to Enterobacteria phage T4 gene y13K, which is also referred to in the lysis literature as pseT.3 and is experimentally and bioinformatically identified as the Rz-equivalent inner-membrane spanin (i-spanin) subunit of a two-component spanin system. This identification is supported by primary T4 genetics and by multiple authoritative reviews that explicitly place pseT.3 as the i-spanin partner of pseT.2 (the Rz1-equivalent outer-membrane lipoprotein; o-spanin) in a separated gene architecture. (summer2007rzrz1lysisgene pages 5-7, summer2007rzrz1lysisgene pages 3-4, catalao2013diversityinbacterial pages 10-11, young2014phagelysisthree pages 5-7)

1) Key concepts and definitions (current understanding)

1.1 Phage lysis as a multi-barrier problem

For Gram-negative hosts, productive phage infection ends with release of progeny through three envelope barriers: inner membrane (IM), peptidoglycan (PG), and outer membrane (OM). Canonical dsDNA phages typically encode a timed system with:
- holin (IM permeabilization; timing gate),
- endolysin (PG degradation), and
- spanin(s) for OM disruption, which is required because PG removal alone can leave intact OM-bounded “spherical” cells that do not burst. (cahill2019phagelysismultiple pages 18-21, young2014phagelysisthree pages 11-12)

1.2 Spanins: definition and architectures

Spanins are phage-encoded lysis proteins that execute the terminal OM disruption step. Two main forms exist:
- Two-component spanins (2CS): an i-spanin (integral IM protein, Rz-like) plus an o-spanin (OM lipoprotein, Rz1-like) that together span the periplasm.
- Unimolecular spanins (u-spanins): single polypeptides bearing an OM lipoprotein signal and a C-terminal IM transmembrane domain, satisfying the same topology constraints in one chain.
T4’s spanin system is a 2CS with separated gene architecture (distinct ORFs), whereas phage λ is the classic embedded architecture (Rz1 encoded entirely within Rz in a different frame). (young2014phagelysisthree pages 5-7, kongari2018phagespaninsdiversity pages 1-2)

2) Functional annotation of T4 y13K (pseT.3): role, process, localization

2.1 Primary function and biological process

y13K/pseT.3 (UniProt P39504) functions as the i-spanin subunit in the T4 spanin complex that is required for outer-membrane disruption during the final step of host cell lysis. This places y13K in the late infection program that coordinates envelope destruction downstream of holin/endolysin activity. (summer2007rzrz1lysisgene pages 5-7, burch2011thebacteriophaget4 pages 1-2, cahill2019phagelysismultiple pages 18-21)

2.2 Partner protein and complex organization

In T4, pseT.3 (i-spanin; y13K) is paired with the adjacent gene pseT.2 (o-spanin). The pair was explicitly cataloged as Rz/Rz1 equivalents (spanins) in the original comparative/genetic study that introduced the “separated” architecture class and listed T4 as a representative example. (summer2007rzrz1lysisgene pages 5-7, summer2007rzrz1lysisgene pages 2-3, young2014phagelysisthree pages 5-7)

2.3 Subcellular localization and topology

Spanin function is fundamentally topological:
- PseT.3 (y13K) carries an N-terminal transmembrane domain, consistent with an inner-membrane anchor and a periplasm-facing domain.
- PseT.2 carries a signal sequence for an outer-membrane lipoprotein, consistent with an o-spanin tethered to the OM.
Together, these features match the defining two-component spanin topology spanning the periplasm and physically linking IM and OM. (summer2007rzrz1lysisgene pages 3-4, summer2007rzrz1lysisgene pages 2-3, catalao2013diversityinbacterial pages 10-11)

3) Evidence: gene-specific experimental validation in T4

3.1 T4 Δ(pseT.3 pseT.2) phenotype: Mg2+-dependent lysis defect

A key defining experimental result is that deletion of the non-overlapping gene pair pseT.3/pseT.2 in T4 produces the classical divalent cation (Mg2+)-dependent lysis defect known for λ Rz/Rz1 mutants: infected cells undergo PG removal but fail to complete OM disruption efficiently under Mg2+-supplemented conditions, forming spherical cells and yielding small plaques/plating defects. This phenotype is strong functional evidence that pseT.3 (y13K) and pseT.2 are bona fide spanin equivalents in T4 rather than unrelated membrane proteins. (summer2007rzrz1lysisgene pages 3-4, summer2007rzrz1lysisgene pages 1-2)

3.2 Genomic deletion details (reproducibility)

The same study reports construction and verification details for the T4 deletion: a recombination construct spanning nt 134,678–136,253 with an internal deletion nt 135,165–135,726, generating a T4 ΔrI Δ(pseT.3 pseT.2) recombinant confirmed by PCR and sequencing and tested under different Mg2+ conditions. (summer2007rzrz1lysisgene pages 12-13)

4) Mechanism: how spanins disrupt the outer membrane

4.1 Dominant model: inner–outer membrane fusion gated by peptidoglycan degradation

The current mainstream mechanistic model is that spanins act as fusogens: they accumulate as IM–OM bridging complexes but are restrained by intact PG (which prevents lateral diffusion/oligomerization). Once endolysin-mediated PG degradation occurs, spanins are “gated” into an active state where oligomerization and conformational rearrangements drive IM–OM fusion, catastrophically compromising the OM barrier and allowing explosive lysis. This model is strongly supported by primary experiments on λ spanins (spheroplast fusion assays; correlation of fusion and lysis defects with spanin missense alleles) and by synthesis in authoritative reviews. T4 spanins are considered mechanistically analogous at the functional level, with direct T4 evidence supporting the same OM-step requirement (Mg2+-dependent spanin phenotype) even though detailed structural dynamics are better studied in λ. (rajaure2015membranefusionduring pages 1-2, rajaure2015membranefusionduring pages 2-3, young2014phagelysisthree pages 11-12)

4.2 Structural/biophysical evidence relevant to the fusion model

Multiple lines of evidence support the fusion concept for two-component spanins generally: purification and imaging of soluble domains yielding rod-like assemblies matching periplasmic dimensions, disulfide-linked dimerization requirements in vivo, and in vitro assays showing lipid/content mixing consistent with fusogenic behavior. Importantly, OM disruption requires correct IM/OM topology—mislocalization of spanin subunits can preserve complex formation yet abolish lytic function, consistent with a mechanism dependent on physical bridging and membrane juxtaposition. (young2014phagelysisthree pages 9-11, cahill2019phagelysismultiple pages 21-24, young2014phagelysisthree pages 8-9)

5) Quantitative data and statistics from comparative studies

5.1 Prevalence of spanins across phage genomes

A large comparative analysis of 677 dsDNA phage genomes infecting Gram-negative hosts reported spanins in >85% of genomes, identifying:
- 528 two-component spanin systems and
- 58 unimolecular spanins,
with two-component architectures broken down into 182 embedded, 228 overlapped, and 118 separated systems. (kongari2018phagespaninsdiversity pages 4-5, kongari2018phagespaninsdiversity pages 22-23)

A separate earlier survey of 137 phage genomes found Rz/Rz1-equivalent systems in the vast majority and described a “separated” architecture class including T4 plus 17 additional genomes (18 separated pairs in that dataset). (summer2007rzrz1lysisgene pages 2-3)

5.2 Diversity and family structure (including T4-like spanins)

Using clustering (40% identity over 40% length), the spanin database work grouped sequences into 143 i-spanin families, 125 o-spanin families, and 13 u-spanin families, with >40% of families being singletons (very high diversity). (kongari2018phagespaninsdiversity pages 1-2)

Notably, this analysis reports that T4-like spanins are abundant and form large families in the separated class; one summary highlights a T4 family with 47 members among abundant spanin families, indicating that T4-like spanin modules recur across related phage lineages even when sequence similarity to λ spanins is limited. (kongari2018phagespaninsdiversity pages 5-7, kongari2018phagespaninsdiversity pages 9-11)

6) Recent developments (prioritizing 2023–2024)

Direct 2023–2024 primary research specifically on T4 y13K/pseT.3 is limited in the retrieved literature; recent work in the spanin field has instead emphasized applications and delivery platforms and broader synthetic biology contexts.

6.1 2024: spanins repurposed as antibacterial payloads

A 2024 study systematically compared phage lysis proteins and found a T1 phage-derived spanin (a u-spanin) had strong intracellular bactericidal activity and broad effectiveness across clinical Gram-negative isolates. Reported testing included 111 E. coli, plus Klebsiella, Pseudomonas aeruginosa, and Acinetobacter isolates; the authors also developed a non-proliferative engineered phage capsid delivery approach to introduce and express the spanin gene in target bacteria. Although not T4-specific, this illustrates a 2024 “real-world implementation” direction where spanin biology inspires new antimicrobial modalities. (yamashita2024harnessingat1 pages 1-2, yamashita2024harnessingat1 pages 8-9)

6.2 2024: programmed autolysis and engineering contexts

A 2024 review of bacterial programmed autolysis in biomanufacturing contexts explicitly notes that phage systems such as λ and T4 require holin–endolysin–spanin for complete lysis, reflecting spanins’ growing role as parts lists for engineered cell-disruption systems. (yamashita2024harnessingat1 pages 8-9)

7) Expert synthesis and authoritative interpretation

Across high-citation reviews and mechanistic primary literature, expert consensus positions spanins as the fourth functional class of phage lysis proteins (alongside holins and endolysins) required in many Gram-negative infections for OM disruption, with the dominant mechanistic interpretation being PG-gated IM–OM fusion. The inclusion of T4 pseT.3/pseT.2 as the exemplar separated architecture in authoritative lysis syntheses reflects the field’s view that T4 uses the same functional solution to the OM barrier despite divergent sequence. (young2014phagelysisthree pages 5-7, young2014phagelysisthree pages 11-12)

8) Practical functional annotation summary (actionable)

A compact summary of identifiers, function, localization, mechanism, evidence, and quantitative context is provided below.

Table: This table summarizes the verified identity, function, topology, mechanism, and T4-specific evidence for bacteriophage T4 gene y13K (UniProt P39504), also known as pseT.3. It is useful as a compact annotation record linking the gene to the two-component spanin system and the experimental lysis phenotype that supports this assignment.

9) Conclusions (functional annotation)

y13K (pseT.3; UniProt P39504) encodes the inner membrane spanin subunit (i-spanin) of bacteriophage T4. Together with pseT.2 (o-spanin) it forms a two-component periplasm-spanning complex required for the terminal outer membrane disruption step of lysis. Genetic deletion of the pseT.3/pseT.2 pair causes the hallmark Mg2+-dependent lysis defect and spherical-cell phenotype that defines loss of spanin function in Gram-negative hosts, validating the annotation. Mechanistically, the most supported model across the spanin field is that spanins drive IM–OM fusion after PG degradation gates activation, providing a coherent interpretation for y13K’s role even where T4-specific structural data are sparse. (summer2007rzrz1lysisgene pages 3-4, summer2007rzrz1lysisgene pages 12-13, rajaure2015membranefusionduring pages 1-2)

References

1. (summer2007rzrz1lysisgene pages 5-7): Elizabeth J. Summer, Joel Berry, Tram Anh T. Tran, Lili Niu, Douglas K. Struck, and Ry Young. Rz/rz1 lysis gene equivalents in phages of gram-negative hosts. Journal of molecular biology, 373 5:1098-112, Nov 2007. URL: https://doi.org/10.1016/j.jmb.2007.08.045, doi:10.1016/j.jmb.2007.08.045. This article has 222 citations and is from a domain leading peer-reviewed journal.

2. (summer2007rzrz1lysisgene pages 3-4): Elizabeth J. Summer, Joel Berry, Tram Anh T. Tran, Lili Niu, Douglas K. Struck, and Ry Young. Rz/rz1 lysis gene equivalents in phages of gram-negative hosts. Journal of molecular biology, 373 5:1098-112, Nov 2007. URL: https://doi.org/10.1016/j.jmb.2007.08.045, doi:10.1016/j.jmb.2007.08.045. This article has 222 citations and is from a domain leading peer-reviewed journal.

3. (catalao2013diversityinbacterial pages 10-11): Maria João Catalão, Filipa Gil, José Moniz-Pereira, Carlos São-José, and Madalena Pimentel. Diversity in bacterial lysis systems: bacteriophages show the way. FEMS microbiology reviews, 37 4:554-71, Jul 2013. URL: https://doi.org/10.1111/1574-6976.12006, doi:10.1111/1574-6976.12006. This article has 339 citations and is from a domain leading peer-reviewed journal.

4. (young2014phagelysisthree pages 5-7): Ryland Young. Phage lysis: three steps, three choices, one outcome. Journal of Microbiology, 52:243-258, Mar 2014. URL: https://doi.org/10.1007/s12275-014-4087-z, doi:10.1007/s12275-014-4087-z. This article has 596 citations and is from a peer-reviewed journal.

5. (cahill2019phagelysismultiple pages 18-21): Jesse Cahill and Ry Young. Phage lysis: multiple genes for multiple barriers. Advances in virus research, 103:33-70, Jan 2019. URL: https://doi.org/10.1016/bs.aivir.2018.09.003, doi:10.1016/bs.aivir.2018.09.003. This article has 350 citations and is from a peer-reviewed journal.

6. (young2014phagelysisthree pages 11-12): Ryland Young. Phage lysis: three steps, three choices, one outcome. Journal of Microbiology, 52:243-258, Mar 2014. URL: https://doi.org/10.1007/s12275-014-4087-z, doi:10.1007/s12275-014-4087-z. This article has 596 citations and is from a peer-reviewed journal.

7. (kongari2018phagespaninsdiversity pages 1-2): Rohit Kongari, Manoj Rajaure, J. Cahill, Eric Rasche, Eleni M. Mijalis, Joel D. Berry, and R. Young. Phage spanins: diversity, topological dynamics and gene convergence. BMC Bioinformatics, Sep 2018. URL: https://doi.org/10.1186/s12859-018-2342-8, doi:10.1186/s12859-018-2342-8. This article has 144 citations and is from a peer-reviewed journal.

8. (burch2011thebacteriophaget4 pages 1-2): L. Burch, Leilei Zhang, Frank G Chao, Hong Xu, and J. Drake. The bacteriophage t4 rapid-lysis genes and their mutational proclivities. Journal of Bacteriology, 193:3537-3545, May 2011. URL: https://doi.org/10.1128/jb.00138-11, doi:10.1128/jb.00138-11. This article has 23 citations and is from a peer-reviewed journal.

9. (summer2007rzrz1lysisgene pages 2-3): Elizabeth J. Summer, Joel Berry, Tram Anh T. Tran, Lili Niu, Douglas K. Struck, and Ry Young. Rz/rz1 lysis gene equivalents in phages of gram-negative hosts. Journal of molecular biology, 373 5:1098-112, Nov 2007. URL: https://doi.org/10.1016/j.jmb.2007.08.045, doi:10.1016/j.jmb.2007.08.045. This article has 222 citations and is from a domain leading peer-reviewed journal.

10. (summer2007rzrz1lysisgene pages 1-2): Elizabeth J. Summer, Joel Berry, Tram Anh T. Tran, Lili Niu, Douglas K. Struck, and Ry Young. Rz/rz1 lysis gene equivalents in phages of gram-negative hosts. Journal of molecular biology, 373 5:1098-112, Nov 2007. URL: https://doi.org/10.1016/j.jmb.2007.08.045, doi:10.1016/j.jmb.2007.08.045. This article has 222 citations and is from a domain leading peer-reviewed journal.

11. (summer2007rzrz1lysisgene pages 12-13): Elizabeth J. Summer, Joel Berry, Tram Anh T. Tran, Lili Niu, Douglas K. Struck, and Ry Young. Rz/rz1 lysis gene equivalents in phages of gram-negative hosts. Journal of molecular biology, 373 5:1098-112, Nov 2007. URL: https://doi.org/10.1016/j.jmb.2007.08.045, doi:10.1016/j.jmb.2007.08.045. This article has 222 citations and is from a domain leading peer-reviewed journal.

12. (rajaure2015membranefusionduring pages 1-2): Manoj Rajaure, Joel Berry, Rohit Kongari, Jesse Cahill, and Ry Young. Membrane fusion during phage lysis. Proceedings of the National Academy of Sciences, 112:5497-5502, Apr 2015. URL: https://doi.org/10.1073/pnas.1420588112, doi:10.1073/pnas.1420588112. This article has 123 citations and is from a highest quality peer-reviewed journal.

13. (rajaure2015membranefusionduring pages 2-3): Manoj Rajaure, Joel Berry, Rohit Kongari, Jesse Cahill, and Ry Young. Membrane fusion during phage lysis. Proceedings of the National Academy of Sciences, 112:5497-5502, Apr 2015. URL: https://doi.org/10.1073/pnas.1420588112, doi:10.1073/pnas.1420588112. This article has 123 citations and is from a highest quality peer-reviewed journal.

14. (young2014phagelysisthree pages 9-11): Ryland Young. Phage lysis: three steps, three choices, one outcome. Journal of Microbiology, 52:243-258, Mar 2014. URL: https://doi.org/10.1007/s12275-014-4087-z, doi:10.1007/s12275-014-4087-z. This article has 596 citations and is from a peer-reviewed journal.

15. (cahill2019phagelysismultiple pages 21-24): Jesse Cahill and Ry Young. Phage lysis: multiple genes for multiple barriers. Advances in virus research, 103:33-70, Jan 2019. URL: https://doi.org/10.1016/bs.aivir.2018.09.003, doi:10.1016/bs.aivir.2018.09.003. This article has 350 citations and is from a peer-reviewed journal.

16. (young2014phagelysisthree pages 8-9): Ryland Young. Phage lysis: three steps, three choices, one outcome. Journal of Microbiology, 52:243-258, Mar 2014. URL: https://doi.org/10.1007/s12275-014-4087-z, doi:10.1007/s12275-014-4087-z. This article has 596 citations and is from a peer-reviewed journal.

17. (kongari2018phagespaninsdiversity pages 4-5): Rohit Kongari, Manoj Rajaure, J. Cahill, Eric Rasche, Eleni M. Mijalis, Joel D. Berry, and R. Young. Phage spanins: diversity, topological dynamics and gene convergence. BMC Bioinformatics, Sep 2018. URL: https://doi.org/10.1186/s12859-018-2342-8, doi:10.1186/s12859-018-2342-8. This article has 144 citations and is from a peer-reviewed journal.

18. (kongari2018phagespaninsdiversity pages 22-23): Rohit Kongari, Manoj Rajaure, J. Cahill, Eric Rasche, Eleni M. Mijalis, Joel D. Berry, and R. Young. Phage spanins: diversity, topological dynamics and gene convergence. BMC Bioinformatics, Sep 2018. URL: https://doi.org/10.1186/s12859-018-2342-8, doi:10.1186/s12859-018-2342-8. This article has 144 citations and is from a peer-reviewed journal.

19. (kongari2018phagespaninsdiversity pages 5-7): Rohit Kongari, Manoj Rajaure, J. Cahill, Eric Rasche, Eleni M. Mijalis, Joel D. Berry, and R. Young. Phage spanins: diversity, topological dynamics and gene convergence. BMC Bioinformatics, Sep 2018. URL: https://doi.org/10.1186/s12859-018-2342-8, doi:10.1186/s12859-018-2342-8. This article has 144 citations and is from a peer-reviewed journal.

20. (kongari2018phagespaninsdiversity pages 9-11): Rohit Kongari, Manoj Rajaure, J. Cahill, Eric Rasche, Eleni M. Mijalis, Joel D. Berry, and R. Young. Phage spanins: diversity, topological dynamics and gene convergence. BMC Bioinformatics, Sep 2018. URL: https://doi.org/10.1186/s12859-018-2342-8, doi:10.1186/s12859-018-2342-8. This article has 144 citations and is from a peer-reviewed journal.

21. (yamashita2024harnessingat1 pages 1-2): Wakana Yamashita, Shinjiro Ojima, Azumi Tamura, Aa Haeruman Azam, Kohei Kondo, Zhang Yuancheng, Longzhu Cui, Masaki Shintani, Masato Suzuki, Yoshimasa Takahashi, Koichi Watashi, Satoshi Tsuneda, and Kotaro Kiga. Harnessing a t1 phage-derived spanin for developing phage-based antimicrobial development. Biodesign Research, 6:0028, Jan 2024. URL: https://doi.org/10.34133/bdr.0028, doi:10.34133/bdr.0028. This article has 13 citations.

22. (yamashita2024harnessingat1 pages 8-9): Wakana Yamashita, Shinjiro Ojima, Azumi Tamura, Aa Haeruman Azam, Kohei Kondo, Zhang Yuancheng, Longzhu Cui, Masaki Shintani, Masato Suzuki, Yoshimasa Takahashi, Koichi Watashi, Satoshi Tsuneda, and Kotaro Kiga. Harnessing a t1 phage-derived spanin for developing phage-based antimicrobial development. Biodesign Research, 6:0028, Jan 2024. URL: https://doi.org/10.34133/bdr.0028, doi:10.34133/bdr.0028. This article has 13 citations.

Artifacts

• Edison artifact artifact-00

Citations

1. kongari2018phagespaninsdiversity pages 1-2
2. catalao2013diversityinbacterial pages 10-11
3. young2014phagelysisthree pages 5-7
4. cahill2019phagelysismultiple pages 18-21
5. young2014phagelysisthree pages 11-12
6. rajaure2015membranefusionduring pages 1-2
7. rajaure2015membranefusionduring pages 2-3
8. young2014phagelysisthree pages 9-11
9. cahill2019phagelysismultiple pages 21-24
10. young2014phagelysisthree pages 8-9
11. kongari2018phagespaninsdiversity pages 4-5
12. kongari2018phagespaninsdiversity pages 22-23
13. kongari2018phagespaninsdiversity pages 5-7
14. kongari2018phagespaninsdiversity pages 9-11
15. https://doi.org/10.1016/j.jmb.2007.08.045;
16. https://doi.org/10.1111/1574-6976.12006
17. https://doi.org/10.1128/JB.00138-11;
18. https://doi.org/10.1016/bs.aivir.2018.09.003
19. https://doi.org/10.1007/s12275-014-4087-z
20. https://doi.org/10.1073/pnas.1420588112;
21. https://doi.org/10.1007/s12275-014-4087-z;
22. https://doi.org/10.1016/j.jmb.2007.08.045
23. https://doi.org/10.1186/s12859-018-2342-8
24. https://doi.org/10.1016/j.jmb.2007.08.045,
25. https://doi.org/10.1111/1574-6976.12006,
26. https://doi.org/10.1007/s12275-014-4087-z,
27. https://doi.org/10.1016/bs.aivir.2018.09.003,
28. https://doi.org/10.1186/s12859-018-2342-8,
29. https://doi.org/10.1128/jb.00138-11,
30. https://doi.org/10.1073/pnas.1420588112,
31. https://doi.org/10.34133/bdr.0028,