agt

UniProt ID: P04519
Organism: Tequatrovirus T4
Review Status: COMPLETE
📝 Provide Detailed Feedback

Gene Description

DNA alpha-glucosyltransferase (AGT; EC 2.4.1.26) is a monomeric, 400-amino-acid GT-B fold glycosyltransferase of bacteriophage T4 that catalyzes the transfer of an alpha-D-glucosyl moiety from UDP-alpha-D-glucose to 5-hydroxymethylcytosine (5hmC) residues in double-stranded T4 DNA. AGT modifies approximately 70% of 5hmC bases in the phage genome in a post-replicative process coupled to DNA synthesis via direct interaction with the T4 sliding clamp protein gp45. Together with DNA beta-glucosyltransferase (Bgt), AGT generates glucosyl-5-hydroxymethylcytosine (glc-HMC) across the viral genome, protecting T4 DNA against phage-encoded cytosine-specific nucleases as well as host restriction-modification and CRISPR-Cas defense systems.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0016740 transferase activity
IEA
GO_REF:0000043 		MODIFY
Summary: Broad keyword-derived annotation; AGT specifically catalyzes DNA alpha-glucosyltransferase activity (GO:0033820).
Reason: While AGT is a transferase, GO:0016740 is overly general because the exact catalytic activity is captured by the descendant term GO:0033820 (DNA alpha-glucosyltransferase activity, EC 2.4.1.26), which is already annotated to this gene.
Supporting Evidence:
file:BPT4/agt/agt-deep-research-falcon.md
T-even phages such as T4 replace cytosine with **5-hydroxymethylcytosine (5hmC/5hmdC)** during DNA replication and then further **glucosylate** this modified base to form **glucosylated 5hmdC (5ghmdC)**
file:BPT4/agt/agt-uniprot.txt
Catalyzes the transfer of glucose from uridine diphosphoglucose to 5-hydroxymethyl cytosine of T4 DNA to yield glucosyl 5-hydroxymethyl cytosine (glc-HMC) (PubMed:15381072).
GO:0016757 glycosyltransferase activity
IEA
GO_REF:0000043 		MODIFY
Summary: Correct parent term but less specific than GO:0033820 (DNA alpha-glucosyltransferase activity).
Reason: AGT is a GT-B fold glycosyltransferase, but the more specific descendant term GO:0033820 (DNA alpha-glucosyltransferase activity) is experimentally established and already present on the gene.
Supporting Evidence:
file:BPT4/agt/agt-deep-research-falcon.md
T-even phages such as T4 replace cytosine with **5-hydroxymethylcytosine (5hmC/5hmdC)** during DNA replication and then further **glucosylate** this modified base to form **glucosylated 5hmdC (5ghmdC)**
file:BPT4/agt/agt-uniprot.txt
Reaction=Transfers an alpha-D-glucosyl residue from UDP-glucose to a hydroxymethylcytosine residue in DNA.; EC=2.4.1.26;
GO:0033820 DNA alpha-glucosyltransferase activity
IEA
GO_REF:0000003 		ACCEPT
Summary: Accurately captures the core enzymatic activity of AGT (EC 2.4.1.26).
Reason: Biochemical and structural studies establish that AGT transfers an alpha-D-glucosyl group from UDP-glucose to 5-hydroxymethylcytosine residues in double-stranded T4 DNA.
Supporting Evidence:
file:BPT4/agt/agt-deep-research-falcon.md
T-even phages such as T4 replace cytosine with **5-hydroxymethylcytosine (5hmC/5hmdC)** during DNA replication and then further **glucosylate** this modified base to form **glucosylated 5hmdC (5ghmdC)**
file:BPT4/agt/agt-uniprot.txt
Reaction=Transfers an alpha-D-glucosyl residue from UDP-glucose to a hydroxymethylcytosine residue in DNA.; EC=2.4.1.26;
GO:0039504 symbiont-mediated suppression of host adaptive immune response
IEA
GO_REF:0000043 		MODIFY
Summary: General keyword-mapped term that should be refined to the specific descendant GO:0098672 (symbiont-mediated suppression of host CRISPR-cas system).
Reason: In bacterial hosts, adaptive immunity corresponds to the CRISPR-Cas system, and the more specific descendant term GO:0098672 is already annotated to this gene based on protection of glucosylated 5hmC DNA against Cas9 cleavage.
Supporting Evidence:
file:BPT4/agt/agt-deep-research-falcon.md
In 2024 experimental work aimed at engineering T4, authors reiterate that 5ghmdC modifications impede recognition/targeting by host nucleases and CRISPR-Cas systems, motivating strategies to transiently reduce modification for genome editing
file:BPT4/agt/agt-uniprot.txt
The glc-HMC modification also protects against the host CRISPR-Cas9 defense system (PubMed:26081634).
GO:0052031 symbiont-mediated perturbation of host defense response
IEA
GO_REF:0000043 		MODIFY
Summary: Broad parent process term that should be refined to the specific host defense evasion terms GO:0099018 and GO:0098672.
Reason: Glucosylation of 5hmC in T4 DNA specifically counteracts host restriction-modification systems (GO:0099018) and CRISPR-Cas interference (GO:0098672), both of which are already present on the gene.
Supporting Evidence:
file:BPT4/agt/agt-deep-research-falcon.md
Glucosylation of 5hmdC is described as a defensive strategy: these bulky glycosyl modifications **protect phage DNA from host nucleases** and help distinguish phage DNA from host DNA
file:BPT4/agt/agt-uniprot.txt
The glc-HMC modification protects the phage genome against its own nucleases and the host restriction endonuclease system (PubMed:15381072). The glc-HMC modification also protects against the host CRISPR-Cas9 defense system (PubMed:26081634).
GO:0052170 symbiont-mediated suppression of host innate immune response
IEA
GO_REF:0000043 		MODIFY
Summary: General keyword-mapped term that should be refined to GO:0099018 (symbiont-mediated evasion of host restriction-modification system).
Reason: The specific innate bacterial defense evaded by AGT-mediated DNA alpha-glucosylation is the host restriction-modification system, captured by the descendant term GO:0099018 already annotated to the gene.
Supporting Evidence:
file:BPT4/agt/agt-deep-research-falcon.md
Glucosylation of 5hmdC is described as a defensive strategy: these bulky glycosyl modifications **protect phage DNA from host nucleases** and help distinguish phage DNA from host DNA
file:BPT4/agt/agt-uniprot.txt
The glc-HMC modification protects the phage genome against its own nucleases and the host restriction endonuclease system (PubMed:15381072).
GO:0098672 symbiont-mediated suppression of host CRISPR-cas system
IEA
GO_REF:0000043 		ACCEPT
Summary: Supported biological role of AGT-mediated DNA glucosylation in protecting phage DNA from CRISPR-Cas9 cleavage.
Reason: Alpha-glucosylation of 5hmC residues in T4 DNA sterically hinders recognition and cleavage by host CRISPR-Cas endonucleases.
Supporting Evidence:
file:BPT4/agt/agt-deep-research-falcon.md
In 2024 experimental work aimed at engineering T4, authors reiterate that 5ghmdC modifications impede recognition/targeting by host nucleases and CRISPR-Cas systems, motivating strategies to transiently reduce modification for genome editing
file:BPT4/agt/agt-uniprot.txt
The glc-HMC modification also protects against the host CRISPR-Cas9 defense system (PubMed:26081634).
GO:0099018 symbiont-mediated evasion of host restriction-modification system
IEA
GO_REF:0000043 		ACCEPT
Summary: Core biological role of AGT-catalyzed DNA alpha-glucosylation in evading host restriction endonucleases.
Reason: Conversion of 5hmC to alpha-glucosyl-5hmC in T4 DNA blocks cleavage by host restriction-modification systems that target unmodified or non-glucosylated DNA.
Supporting Evidence:
file:BPT4/agt/agt-deep-research-falcon.md
Glucosylation of 5hmdC is described as a defensive strategy: these bulky glycosyl modifications **protect phage DNA from host nucleases** and help distinguish phage DNA from host DNA
file:BPT4/agt/agt-uniprot.txt
The glc-HMC modification protects the phage genome against its own nucleases and the host restriction endonuclease system (PubMed:15381072).
GO:0006304 DNA modification
IEA
GO_REF:0000041 		ACCEPT
Summary: Directly describes the post-replicative covalent glucosylation of 5hmC in T4 genomic DNA.
Reason: AGT covalently modifies 5-hydroxymethylcytosine bases in newly synthesized T4 dsDNA by transferring an alpha-D-glucosyl moiety from UDP-glucose.
Supporting Evidence:
file:BPT4/agt/agt-deep-research-falcon.md
T-even phages such as T4 replace cytosine with **5-hydroxymethylcytosine (5hmC/5hmdC)** during DNA replication and then further **glucosylate** this modified base to form **glucosylated 5hmdC (5ghmdC)**
file:BPT4/agt/agt-uniprot.txt
Catalyzes the transfer of glucose from uridine diphosphoglucose to 5-hydroxymethyl cytosine of T4 DNA to yield glucosyl 5-hydroxymethyl cytosine (glc-HMC) (PubMed:15381072).
GO:0033820 DNA alpha-glucosyltransferase activity
IDA
PMID:6078540
On the specificity of bacteriophage-induced hydroxymethylcyt... 		ACCEPT
Summary: Direct experimental annotation for AGT's enzymatic activity on 5hmC-containing DNA.
Reason: de Waard et al. (1967) and subsequent biochemical and crystallographic studies directly establish that AGT is the T4-induced hydroxymethylcytosine alpha-glucosyltransferase.
Supporting Evidence:
PMID:6078540
On the specificity of bacteriophage-induced hydroxymethylcytosine glucosyltransferases. II. Specificities of hydroxymethylcytosine alphaand beta-glucosyltransferases induced by bacteriophage T4.
file:BPT4/agt/agt-deep-research-falcon.md
T-even phages such as T4 replace cytosine with **5-hydroxymethylcytosine (5hmC/5hmdC)** during DNA replication and then further **glucosylate** this modified base to form **glucosylated 5hmdC (5ghmdC)**

Core Functions

Catalyzes the post-replicative transfer of an alpha-D-glucosyl moiety from UDP-alpha-D-glucose onto 5-hydroxymethylcytosine residues in T4 double-stranded DNA, thereby modifying the viral genome to evade host restriction-modification and CRISPR-Cas nucleases.

Molecular Function:
DNA alpha-glucosyltransferase activity
Directly Involved In:
DNA modification symbiont-mediated evasion of host restriction-modification system symbiont-mediated suppression of host CRISPR-cas system
Supporting Evidence:
  • file:BPT4/agt/agt-deep-research-falcon.md
    T-even phages such as T4 replace cytosine with **5-hydroxymethylcytosine (5hmC/5hmdC)** during DNA replication and then further **glucosylate** this modified base to form **glucosylated 5hmdC (5ghmdC)**
  • file:BPT4/agt/agt-uniprot.txt
    Catalyzes the transfer of glucose from uridine diphosphoglucose to 5-hydroxymethyl cytosine of T4 DNA to yield glucosyl 5-hydroxymethyl cytosine (glc-HMC) (PubMed:15381072).

References

Loading supporting content…

Download this section (compressed HTML)

Suggested Questions for Experts

Q: How is substrate site selection partitioned between AGT (~70% alpha-glucosylation) and BGT (~30% beta-glucosylation) on nascent 5hmC-containing T4 DNA during gp45-coupled replication?

Q: What is the structural basis of the interaction between AGT and the T4 sliding clamp gp45?

Suggested Experiments

Experiment: Determine the cryo-EM or crystal structure of AGT bound to the T4 gp45 sliding clamp and a 5hmC-containing dsDNA substrate to define how clamp recruitment coordinates post-replicative alpha-glucosylation.

Experiment: Perform single-molecule nanopore sequencing of nascent T4 replication forks in wild-type, agt-null, and bgt-null backgrounds to map the kinetics and sequence context of alpha- versus beta-glucosylation in vivo.

Deep Research

Falcon

(agt-deep-research-falcon.md)

Loading supporting content…

Download this section (compressed HTML)

📚 Additional Documentation

Notes

(agt-notes.md)

Loading supporting content…

Download this section (compressed HTML)

📄 View Raw YAML

Loading supporting content…

Download this section (compressed HTML)