Protein ac (gp52.2) is a 51-amino-acid predicted two-pass integral membrane protein of bacteriophage T4 that localizes to the host Escherichia coli membrane. Wild-type protein ac alters host membrane permeability and promotes cellular accumulation of acridine dyes such as acriflavin, rendering phage development sensitive to acridine inhibition; conversely, loss-of-function mutations in gene ac reduce acridine uptake and confer resistance to acridine-mediated inhibition of T4 development. Its precise molecular function during normal phage infection in the absence of acridines remains uncharacterized.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0033644 host cell membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Protein ac (gp52.2) is a 51-residue hydrophobic protein predicted to insert into the host bacterial membrane as a multi-pass transmembrane protein, consistent with its role in modulating host membrane permeability to acridines. Reason: Sequence architecture (two transmembrane helices) and physiological evidence showing altered acriflavin flux across the infected Escherichia coli cell envelope support localization to the host cell membrane (GO:0033644). Supporting Evidence: file:BPT4/ac/ac-uniprot.txt SUBCELLULAR LOCATION: Host membrane {ECO:0000305}; Multi-pass membrane protein {ECO:0000305}. file:BPT4/ac/ac-deep-research-falcon.md **Acriflavin inhibits T4 development**, and **mutations in the T4 ac gene (gene 52.2) overcome acriflavin inhibition and allow phage development** |
| GO:0046677 response to antibiotic | IEA GO_REF:0000043 | REMOVE | Summary: Wild-type protein ac does not mediate a protective response to antibiotics; instead, loss-of-function mutations in gene ac confer resistance to acridine dyes by preventing wild-type ac-dependent acridine uptake. Reason: This annotation is a UniProt keyword-mapping artifact derived from the disruption phenotype of ac mutants. Wild-type gp52.2 increases sensitivity of phage development to acriflavin (an intercalating acridine dye) rather than mediating a response to antibiotics, and resistance arises only when gene ac is mutated or inactivated. Supporting Evidence: file:BPT4/ac/ac-uniprot.txt DISRUPTION PHENOTYPE: Mutations in the gene confer resistance to acridine-inhibition of phage development. {ECO:0000269|PubMed:9560385}. file:BPT4/ac/ac-deep-research-falcon.md **Acriflavin inhibits T4 development**, and **mutations in the T4 ac gene (gene 52.2) overcome acriflavin inhibition and allow phage development** |
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Download this section (compressed HTML)Q: Does gp52.2 (protein ac) form an oligomeric ion or small-molecule channel in the Escherichia coli inner membrane itself, or does it inhibit a host multidrug efflux pump (such as AcrAB-TolC) to cause intracellular acridine accumulation?
Q: What selective advantage does gene ac provide to bacteriophage T4 in natural polymicrobial environments where acridines are absent?
Experiment: Measure ethidium bromide and acriflavin influx and efflux rates in wild-type vs delta-acrAB-tolC Escherichia coli strains expressing T4 gene ac (52.2) from an inducible plasmid.
Hypothesis: Protein ac either directly permeabilizes the inner membrane independent of AcrAB-TolC or inhibits AcrB-mediated efflux of planar cationic dyes.
Experiment: Perform affinity purification Coupled to mass spectrometry (AP-MS) of epitope-tagged gp52.2 solubilized from T4-infected E. coli inner membranes.
Hypothesis: gp52.2 interacts with a specific host inner-membrane transporter or phage co-factor (such as theama/rII membrane proteins) to modulate envelope energetics during infection.
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