| Study | Organism / phage context | Experimental approach | Main findings relevant to AdfA | Functional annotation / localization implication | DOI / URL | Publication date |
|---|---|---|---|---|---|---|
| LeRoux et al. 2022 | *E. coli* DarTG1 defense; phage RB69 with comparison to T4/T6 homologs | Experimental evolution of RB69 on DarTG1 cells; sequencing of escape mutants; ectopic expression of RB69 gp61.2(R164H) and T4 homolog; EOP assays; ELTA-based DNA ADP-ribosylation assay; growth rescue upon DarT1 expression; T4 61.2 knockout/stop-codon tests | Four independent DarTG1-resistant RB69 clones carried mutations in the same codon of phage gene 61.2 (R164H or R164S). Ectopic expression of RB69 gp61.2(R164H) or the T4 homolog improved RB69 EOP on DarTG1 hosts. No detectable DNA ADP-ribosylation was seen in cells infected with evolved RB69 carrying gp61.2(R164H), and gp61.2(R164H) restored growth to cells producing DarT1. Gene 61.2 was therefore renamed **adfA** (anti-DarT factor A). T4 61.2 was nonessential for plaquing without DarTG1. (pqac-00000003, pqac-00000008, pqac-00000012, pqac-00000013, pqac-00000019) | Strong evidence that AdfA is a phage-encoded anti-DarT factor acting in the infected bacterial cytoplasm during infection to prevent DarT-mediated ADP-ribosylation of phage DNA; likely a counter-defense protein rather than a core virion or replication enzyme. Conserved position near **dmd** suggests an anti-TA/anti-defense locus in T-even phages. (pqac-00000003, pqac-00000012, pqac-00000013) | DOI: 10.1038/s41564-022-01153-5; https://doi.org/10.1038/s41564-022-01153-5 | Jun 2022 |
| Patel & Seed 2024 | Clinical *Vibrio cholerae* isolates with DarTG defense; phage ICP1; compares with RB69/T4/T6 AdfA-like alleles | Characterization of phage antitoxin mimic AdfB; infection timing / expression analysis; comparative discussion of AdfA alleles in RB69, T4, T6 | AdfB is expressed early in infection (before and peaking by ~8 min) and likely antagonizes DarT through direct interaction. The paper cites AdfA in RB69/T4/T6 as an analogous phage-encoded anti-DarT factor with active and inactive alleles, supporting the idea that Adf proteins are phage antitoxin mimics shaped by prior exposure to DarTG systems. (pqac-00000014, pqac-00000016, pqac-00000026) | Although this study focuses on AdfB, it supports AdfA annotation as a small anti-DarT counter-defense protein that functions early during infection in the bacterial cytoplasm, likely by directly targeting the toxin rather than modifying DNA itself. It also supports allele-specific adaptation of Adf factors in natural phage-host arms races. (pqac-00000014, pqac-00000016, pqac-00000026) | DOI: 10.1128/mbio.00111-24; https://doi.org/10.1128/mbio.00111-24 | Oct 2024 |
| Johannesman et al. 2025 preprint | T4-like / Tevenvirinae phages including T4, T2, RB69; DarTG1 and DarTG2 defense contexts | Comparative genetics across T-even phages; adfA deletion analysis in T4; bacterial two-hybrid assays; ectopic expression; identification of additional anti-DarT factor AdfN | AdfA is described as a small non-enzymatic anti-DarT factor lacking recognizable enzymatic domains. Bacterial two-hybrid assays support toxin association: RB69 AdfA(R164H) shows strong association with DarT1, while T4 AdfA shows weaker interaction. However, **T4 ΔadfA** remains resistant to DarTG1, showing AdfA is dispensable for T4 resistance because T4 also carries **AdfN**, a NADAR-family DNA ADP-ribosylglycohydrolase that is necessary/sufficient for major anti-DarTG1 activity in T-even phages. Presence of AdfA homologs alone does not predict resistance. (pqac-00000017, pqac-00000021, pqac-00000022, pqac-00000024, pqac-00000025) | Refines annotation: T4 AdfA should be annotated as a probable anti-DarT factor acting through protein-protein interaction with DarT during infection, but not necessarily the dominant anti-DarTG1 determinant in T4. Localization is again most consistent with action in the infected host-cell cytoplasm on the DarT defense machinery and/or at phage DNA replication sites. (pqac-00000021, pqac-00000022, pqac-00000024) | DOI: 10.1101/2024.07.11.602962; https://doi.org/10.1101/2024.07.11.602962 | Jul 2025 preprint |


*Table: This table compiles the main experimental evidence supporting annotation of phage gene 61.2/AdfA as an anti-DarT factor, while distinguishing direct evidence from comparative inference. It also highlights that in T4, AdfA appears dispensable because additional anti-DarTG factors such as AdfN contribute to resistance.*