| Aspect | Evidence-backed summary | Key source(s) |
|---|---|---|
| identity/domains | **Verified target:** Enterobacteria phage T4 **gene 46 / gp46** corresponds to the **Rad50 homolog** of the T4 gp46/gp47 DNA end-processing complex, matching the UniProt P04522 context. Biochemical and genetic literature consistently treats gp46 as an **ABC/SMC-like ATPase** with a conserved nucleotide-binding domain; this aligns with UniProt/InterPro assignment to **P-loop NTPase / Rad50-SbcC AAA+ family**. | Herdendorf & Nelson 2014, *Biochemistry*, doi:10.1021/bi500558d, https://doi.org/10.1021/bi500558d; Albrecht et al. 2012, *J Biol Chem*, doi:10.1074/jbc.M112.392316, https://doi.org/10.1074/jbc.M112.392316 (pqac-00000004, pqac-00000006) |
| complex partners | gp46 functions with **gp47 (the T4 Mre11 homolog)** as the T4 **MR complex**; biochemical interaction data also support association of gp46/gp47 with **UvsY**, linking DNA end resection to presynaptic filament assembly during recombination. | Bleuit et al. 2001, *PNAS*, doi:10.1073/pnas.131007498, https://doi.org/10.1073/pnas.131007498; Albrecht et al. 2012, *J Biol Chem*, https://doi.org/10.1074/jbc.M112.392316 (pqac-00000008, pqac-00000006, pqac-00000012) |
| enzymatic activities | The **primary catalytic activity of the complex is 5′→3′ dsDNA exonuclease activity**, genetically assigned to gp46/gp47 and biochemically observed in reconstituted assays; **gp46 itself is also an ATP-binding/hydrolyzing enzyme** whose ATPase is strongly stimulated by gp47 and DNA. Thus, gp46 is best annotated as the **ATPase/structural motor subunit** of an exonuclease complex rather than the nuclease active site itself. | Bleuit et al. 2001, *PNAS*, https://doi.org/10.1073/pnas.131007498; Herdendorf & Nelson 2014, *Biochemistry*, https://doi.org/10.1021/bi500558d (pqac-00000008, pqac-00000004) |
| substrate specificity | Available data support activity on **DNA ends**, especially **double-stranded DNA substrates requiring 5′-strand resection** to generate recombinogenic 3′ ssDNA tails. Structural/mechanistic work indicates Rad50 can partially occlude nuclease sites such that **ssDNA more readily accesses Mre11/gp47 nuclease sites**, consistent with staged processing of DNA ends rather than indiscriminate nucleolysis. | Mosig 1998, *Annu Rev Genet*, doi:10.1146/annurev.genet.32.1.379, https://doi.org/10.1146/annurev.genet.32.1.379; Albrecht et al. 2012, *J Biol Chem*, https://doi.org/10.1074/jbc.M112.392316 (pqac-00000000, pqac-00000003) |
| mechanistic model | Current model: gp46 **binds/hydrolyzes ATP at the Rad50 head dimer interface**; ATP-driven conformational cycling promotes assembly at DNA ends and transitions to a **translocation state** that supports processive nuclease action by gp47. Work on the T4 MR system supports a **two-state mechanism** (initiation/assembly vs translocation), with allosteric communication from gp47 to gp46 required for full ATPase activation. | Albrecht et al. 2012, *J Biol Chem*, https://doi.org/10.1074/jbc.M112.392316; Herdendorf & Nelson 2014, *Biochemistry*, https://doi.org/10.1021/bi500558d (pqac-00000003, pqac-00000004, pqac-00000007) |
| pathway/biological role | gp46 is **essential in vivo** for **homologous recombination**, **double-strand break repair**, and **recombination-dependent DNA replication (RDR)** in bacteriophage T4. Genetic studies show gene 46 mutants are strongly recombination-defective, and plasmid/phage assays place gp46 among the core factors needed to repair DSBs through replication-coupled pathways. | Kreuzer et al. 1995, *J Bacteriol*, doi:10.1128/jb.177.23.6844-6853.1995, https://doi.org/10.1128/jb.177.23.6844-6853.1995; George & Kreuzer 1996, *Genetics*, doi:10.1093/genetics/143.4.1507, https://doi.org/10.1093/genetics/143.4.1507; Mosig 1998, https://doi.org/10.1146/annurev.genet.32.1.379 (pqac-00000002, pqac-00000000) |
| localization/cellular context | No evidence supports a virion structural role or extracellular localization. Function is best placed in the **infected E. coli cytoplasm**, where gp46 acts on **phage DNA replication/recombination intermediates** and damaged DNA ends; older work also reported a **membrane-associated DNase activity controlled by genes 46/47**, but the strongest modern interpretation is a DNA-metabolic role in intracellular nucleoprotein complexes rather than stable membrane localization. | Claudia & Wiberg 1981, *J Virol*, doi:10.1128/JVI.40.1.65-77.1981, https://doi.org/10.1128/JVI.40.1.65-77.1981; Liu & Morrical 2010, *Virology Journal*, doi:10.1186/1743-422X-7-357, https://doi.org/10.1186/1743-422X-7-357 (pqac-00000000, pqac-00000008) |
| key quantitative data | Reported quantitative findings include: **gp46 ATPase kcat ≈ 0.15 s⁻¹ alone** and **≈ 3.2 s⁻¹ with gp47 + dsDNA** (~20-fold activation); ATPase cooperativity increases from **Hill ~1.4 (gp46 alone)** to **~2.4 (MR-D complex)**. In a dsDNA exonuclease assay, retained label fell from **100% control to 44% with gp46 alone** and to **14% with gp46+gp47**, supporting gp47 stimulation of nuclease function. An Mre11-interface mutant reduced dsDNA exonuclease activity by **~10-fold** under processive conditions. | Herdendorf & Nelson 2014, *Biochemistry*, https://doi.org/10.1021/bi500558d; Bleuit et al. 2001, *PNAS*, https://doi.org/10.1073/pnas.131007498; Albrecht et al. 2012, *J Biol Chem*, https://doi.org/10.1074/jbc.M112.392316 (pqac-00000003, pqac-00000004, pqac-00000005, pqac-00000008, pqac-00000012) |
| recent 2023-2024 developments | Direct 2023-2024 gp46-specific primary literature appears limited, but recent cross-system structural work strengthened inference: a **2024 yeast MR cryo-EM study** mapped conserved Rad50 ATP- and DNA-contacting residues and explicitly linked corresponding **T4 gp46 residues** to reduced ATP binding/hydrolysis and defective gp47-dependent nuclease activity, reinforcing mechanistic conservation between phage and eukaryotic MR complexes. | Petrini et al. 2024, *Research Square* preprint, doi:10.21203/rs.3.rs-5390974/v1, https://doi.org/10.21203/rs.3.rs-5390974/v1 (pqac-00000009, pqac-00000010) |
| applications | **No established 2023-2024 biotechnology application specifically uses gp46** itself. Modern T4-derived applications in diagnostics primarily exploit other recombination proteins (**UvsX, UvsY, gp32**) in RPA/SIBA isothermal amplification platforms. Therefore, gp46 is currently more important as a **mechanistic model for MR/Rad50 biology** than as a routine applied reagent. | Morrical 2025, *EcoSal Plus*, doi:10.1128/ecosalplus.esp-0003-2025, https://doi.org/10.1128/ecosalplus.esp-0003-2025; Liu et al. 2024, *Front Cell Infect Microbiol*, doi:10.3389/fcimb.2024.1281827, https://doi.org/10.3389/fcimb.2024.1281827; Anbazhagan et al. 2024, *3 Biotech*, doi:10.1007/s13205-024-04055-x, https://doi.org/10.1007/s13205-024-04055-x (pqac-00000011) |


*Table: This table condenses the strongest evidence on the identity, biochemical role, pathway function, mechanistic model, and recent context for Enterobacteria phage T4 gene 46 (gp46; UniProt P04522). It is useful as a compact functional annotation that distinguishes direct evidence from broader pathway and comparative inferences.*