T4 Dam is a DNA adenine methyltransferase (EC 2.1.1.72) that catalyzes the transfer of a methyl group from S-adenosyl-L-methionine (AdoMet) to the N6 position of adenine within GATC palindromic sequences. The enzyme functions as a monomer and methylates both cytosine- and 5-hydroxymethylcytosine-containing DNA substrates. The primary biological role is to protect phage T4 genomic DNA from degradation by the host E. coli restriction-modification defense system. This is a well-characterized "orphan" methyltransferase with high-resolution crystal structures available (PDB: 1Q0S, 1Q0T, 1YF3).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003676 nucleic acid binding | IEA GO_REF:0000002 | MODIFY | Summary: T4 Dam binds DNA as part of its methyltransferase activity. Crystal structures confirm DNA binding capability [PMID:12937411]. However, "nucleic acid binding" is overly general for a protein with well-characterized DNA-specific binding and enzymatic activity. Reason: This term is too general. The protein specifically binds DNA (not RNA) in a sequence-specific manner (GATC recognition). More specific terms like GO:0003677 (DNA binding) or GO:0043565 (sequence-specific DNA binding) are more informative and are already annotated. Proposed replacements: sequence-specific DNA binding Supporting Evidence: PMID:12937411 T4Dam contains two domains: a seven-stranded catalytic domain that harbors the binding site for AdoHcy and a DNA binding domain file:BPT4/DAM/DAM-deep-research-falcon.md Crystal structures resolved a binary complex (Dam-AdoHcy) and a ternary Dam-DNA-AdoHcy complex |
| GO:0003677 DNA binding | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: T4 Dam binds double-stranded DNA containing GATC sequences. This is well established by crystal structures showing Dam-DNA complexes [PMID:12937411, PMID:15882618] and biochemical studies demonstrating Km for DNA substrate of 1.1 x 10^-12 M [PMID:7782299]. The term is accurate, but it is a broad parent of the more informative DNA methyltransferase functions. Reason: DNA binding is necessary for Dam activity, but it is not the best core annotation for this enzyme. The core function is site-specific DNA adenine methyltransferase activity, with DNA binding as a supporting molecular property. Supporting Evidence: PMID:7782299 the Km for substrate nonglucosylated, unmethylated T4 gt- dam DNA is 1.1 x 10(-12) M PMID:12937411 a DNA binding domain consisting of a five-helix bundle and a beta-hairpin |
| GO:0006260 DNA replication | IEA GO_REF:0000043 | REMOVE | Summary: While T4 Dam methylates newly replicated phage DNA, the enzyme itself is not directly involved in DNA replication (DNA synthesis). Dam acts on DNA after or during replication to provide methylation-based protection, but does not participate in the replication machinery itself. Reason: T4 Dam is not part of the DNA replication machinery. It is a DNA modification enzyme that acts on replicated DNA. The methylation protects DNA from restriction enzymes but does not contribute to DNA synthesis. This appears to be an over-annotation based on the UniProtKB keyword "DNA replication" which may have been applied due to the gene's role in the phage replication cycle rather than the enzymatic mechanism of replication. Supporting Evidence: PMID:2510127 Bacteriophage T4 codes for a DNA-[N6-adenine] methyltransferase (Dam) file:BPT4/DAM/DAM-deep-research-falcon.md T4 Dam is a DNA N6-adenine methyltransferase that transfers a methyl group from S-adenosyl-L-methionine (AdoMet) to the N6 position of adenine within GATC sites |
| GO:0008168 methyltransferase activity | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: T4 Dam is indeed a methyltransferase, specifically a DNA adenine methyltransferase (EC 2.1.1.72). This is experimentally validated [PMID:2510127, PMID:7782299]. Reason: This is accurate but quite general. The more specific term GO:0009007 (site-specific DNA-methyltransferase adenine-specific activity) is also annotated and is more precise. Keeping this general term as a non-core parent is acceptable because it is not incorrect, but it should not be treated as the main curated function. Supporting Evidence: PMID:7782299 The bacteriophage T4 dam gene, encoding the Dam DNA [N6-adenine]methyltransferase (MTase) PMID:2510127 Bacteriophage T4 codes for a DNA-[N6-adenine] methyltransferase (Dam) |
| GO:0009007 site-specific DNA-methyltransferase (adenine-specific) activity | IEA GO_REF:0000120 | ACCEPT | Summary: T4 Dam specifically methylates the N6 position of adenine within GATC sequences. This site-specific adenine methylation activity is the core molecular function of the enzyme, experimentally demonstrated in multiple studies [PMID:2510127, PMID:7782299]. Reason: This is the most precise and accurate molecular function term for T4 Dam. The enzyme recognizes the GATC palindrome and methylates the adenine at N6 position. This is the core enzymatic function and should be retained. Supporting Evidence: PMID:7782299 T4 Dam methylates the palindromic tetranucleotide, GATC, designated the canonical sequence PMID:2510127 Bacteriophage T4 codes for a DNA-[N6-adenine] methyltransferase (Dam) which recognizes primarily the sequence GATC |
| GO:0009307 DNA restriction-modification system | IEA GO_REF:0000002 | MODIFY | Summary: T4 Dam is specifically an "orphan" methyltransferase - it is part of a modification system but lacks a cognate restriction enzyme. The phage uses Dam to protect its DNA FROM host restriction systems, not as part of a complete R-M system of its own. Reason: This term implies Dam is part of a complete restriction-modification system with both restriction and modification activities. T4 Dam is explicitly an orphan methyltransferase (M.EcoT4Dam) that provides DNA protection without an associated restriction enzyme. The appropriate term is GO:0099018 (symbiont-mediated evasion of host restriction-modification system) which accurately describes the protective role against host R-M systems. Proposed replacements: symbiont-mediated evasion of host restriction-modification system Supporting Evidence: file:BPT4/DAM/DAM-deep-research-falcon.md T4 Dam is explicitly an orphan methyltransferase (M.EcoT4Dam) that provides DNA protection without an associated restriction enzyme |
| GO:0016740 transferase activity | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: T4 Dam catalyzes transfer of a methyl group from AdoMet to DNA adenine, which is a transferase reaction. This is accurate but extremely general. Reason: While accurate, this is a very high-level term. More specific terms (GO:0008168 methyltransferase activity, GO:0009007 site-specific DNA-methyltransferase activity) are also present and more informative. Transferase activity is not incorrect, but it should be retained only as a non-core parent term. Supporting Evidence: PMID:7782299 The bacteriophage T4 dam gene, encoding the Dam DNA [N6-adenine]methyltransferase (MTase) |
| GO:0032259 methylation | IEA GO_REF:0000120 | MODIFY | Summary: T4 Dam catalyzes DNA adenine methylation. The enzyme is involved in the biological process of DNA methylation to protect phage DNA. Reason: The annotation is directionally correct but too broad. T4 Dam modifies DNA by site-specific adenine methylation; the best available non-obsolete process replacement is GO:0006304 DNA modification, while the phage-specific outcome is captured by GO:0099018 restriction-modification system evasion. Proposed replacements: DNA modification Supporting Evidence: PMID:2510127 Bacteriophage T4 codes for a DNA-[N6-adenine] methyltransferase (Dam) |
| GO:0052031 symbiont-mediated perturbation of host defense response | IEA GO_REF:0000043 | MODIFY | Summary: This term and its definition ("A process in which a symbiont interferes with the ability of the host to mount a defense in response to its presence") is too broad for the specific biology. T4 Dam does not generally perturb host defense; it methylates phage DNA so the genome can evade host restriction- modification systems. Reason: The broad host-defense framing should be replaced by the mechanistic phage term. The correct term for T4 Dam's role in protecting phage DNA from bacterial restriction enzymes is GO:0099018 (symbiont-mediated evasion of host restriction-modification system), which is already annotated and explicitly covers phages and bacterial restriction systems. Proposed replacements: symbiont-mediated evasion of host restriction-modification system Supporting Evidence: file:BPT4/DAM/DAM-deep-research-falcon.md By methylating GATC, T4 Dam participates in phage counter-defense against host restriction systems |
| GO:0052170 symbiont-mediated suppression of host innate immune response | IEA GO_REF:0000043 | MODIFY | Summary: This term is defined as "A process in which a symbiont inhibits or disrupts the normal execution of the innate immune response of the host organism, the host's first line of defense against infection." This is the wrong level of abstraction for T4 Dam. The supported mechanism is restriction-modification evasion by phage DNA methylation, not general suppression of an innate immune response. Reason: This SPKW-derived annotation conflates phage antirestriction with broad immune-response suppression. Bacteriophage T4 infects Escherichia coli, and the evidence points to a specific bacterial restriction-modification counter- defense mechanism. Replace this row with GO:0099018, which is already present and accurately captures the Dam-mediated phage mechanism. Proposed replacements: symbiont-mediated evasion of host restriction-modification system Supporting Evidence: file:BPT4/DAM/DAM-deep-research-falcon.md T4 Dam acts in the infected E. coli cytoplasm on phage DNA, methylating GATC sites as the genome is replicated |
| GO:0099018 symbiont-mediated evasion of host restriction-modification system | IEA GO_REF:0000043 | ACCEPT | Summary: This is the correct term for T4 Dam's biological role. The GO definition explicitly states: "A process by which a symbiont evades the DNA restriction modification system of its host. This process occurs in phages to protect themselves from bacterial restriction enzyme systems. Some viruses encode their own methyltransferase in order to protect their genome from host restriction enzymes." This precisely describes T4 Dam. Reason: This is the most accurate biological process term for T4 Dam. The enzyme methylates phage DNA to protect it from E. coli restriction enzymes. The term definition explicitly references phages, bacterial restriction systems, and virus-encoded methyltransferases. T4 Dam is a canonical example of this mechanism. Supporting Evidence: file:BPT4/DAM/DAM-deep-research-falcon.md By methylating GATC, T4 Dam participates in phage counter-defense against host restriction systems PMID:12937411 DNA-adenine methylation at certain GATC sites plays a pivotal role in bacterial and phage gene expression |
| GO:0032259 methylation | IMP PMID:2510127 Single amino acid changes that alter the DNA sequence specif... | MODIFY | Summary: This IMP (Inferred from Mutant Phenotype) annotation is based on the Miner et al. 1989 study that characterized dam mutants. The damh mutation (P126S) produces a hypermethylating phenotype, demonstrating the enzyme's role in DNA methylation in vivo. Reason: This experimental annotation is well supported, but the term itself is broader than the biology tested. The mutant phenotype supports DNA modification by T4 Dam, not methylation in an unrestricted substrate/process sense. Use the more specific non-obsolete process term GO:0006304 DNA modification. Proposed replacements: DNA modification Supporting Evidence: PMID:2510127 Hypermethylating mutants, damh, exhibit a relaxation in sequence specificity, that is, they are readily able to methylate non-canonical sites |
| GO:0009008 DNA-methyltransferase activity | IDA PMID:7782299 Phage T4 DNA [N6-adenine]methyltransferase. Overexpression, ... | ACCEPT | Summary: This IDA (Inferred from Direct Assay) annotation is based on the Kossykh et al. 1995 study that overexpressed, purified, and biochemically characterized T4 Dam. The enzyme was shown to have DNA methyltransferase activity with measured kinetic parameters. Reason: This is high-quality experimental evidence. The study purified T4 Dam to near homogeneity and characterized its methyltransferase activity with precise kinetic measurements (Km for AdoMet = 0.1 uM, Km for DNA substrate = 1.1 x 10^-12 M). This directly demonstrates the core molecular function of T4 Dam. Supporting Evidence: PMID:7782299 The Km for the methyl donor, S-adenosylmethionine, is 0.1 x 10(-6) M, and the Km for substrate nonglucosylated, unmethylated T4 gt- dam DNA is 1.1 x 10(-12) M |
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Download this section (compressed HTML)Q: What is the precise timing of Dam methylation during phage infection - does it occur co-replicationally or post-replicationally?
Q: Are there E. coli restriction systems that T4 specifically evades through Dam methylation, and which host strains show differential susceptibility to dam- phage?
Experiment: Systematic analysis of T4 dam- phage viability across E. coli strains with different restriction-modification systems to catalog the protective scope of Dam methylation.
Hypothesis: T4 Dam methylation provides selective protection against specific host restriction systems, and dam- phage will show differential viability depending on the host R-M system present.
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