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Mode of Action (MoA)
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degrades S-adenosyl-methionine (SAM) and inhibits SAM synthase. SAM is believed to be a co-factor in BREX-mediated and RM-mediated exclusion.
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Evidence
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Deletion mutants lacking gene 0.3 encoding S-adenosyl-methionine lyase failed to overcome host restriction and exhibited no detectable SAMase activity in infected E. coli cells (ECO_0001038). Assays of cell extracts infected with various T3 strains showed that wild-type T3 induced strong SAMase activity, while T3 mutants such as R1, R4, R7, R12, and R13 showed both restriction sensitivity and complete loss of SAMase function. An amber mutant (HR2) produced SAMase only in suppressor hosts, confirming gene-linked inactivation. However, strain 3356 retained the ability to overcome restriction despite loss of SAMase activity, indicating that SAMase production is not the sole mechanism for bypassing restriction systems. Electrophoresis of phage-infected protein samples revealed the absence of the 0.3 protein in deletion and amber mutants, directly linking gene 0.3 to SAMase function. The enzyme cleaved radiolabeled S-adenosylmethionine in vitro, forming detectable products by thin-layer chromatography (ECO_0000325), establishing enzymatic activity of the SAMase gene product.
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MoA Category
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degrades or sequesters molecules utilised by host defence systems
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Subtype(s) of the defence system(s) inhibited by the protein
Defence Subtype
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Escherichia coli type I RM;Escherichia coli type I BREX
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Relevant publication(s)
DOI
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10.1128/JVI.19.1.136-145.1976,
10.1016/j.celrep.2023.112972
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Other components of the anti-defence system
Multicomponent System
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-
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Known structure in PDB
PDB ID
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6ZNB
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Genome(s) encoding the protein
Protein Source
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Enterobacteria phage T3
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Defence system(s) inhibited by the protein
Defences
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RM,
BREX
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