darB

Gene Description

DarB is a 251 kDa antirestriction protein from bacteriophage P1 that protects phage DNA from host Type I restriction-modification systems, specifically EcoB and EcoK. The protein contains an N-terminal Type II methyltransferase M.TaqI-like domain and a central DExD-like helicase domain. DarB is incorporated into the phage virion during assembly and is ejected into the host cell cytoplasm along with phage DNA at infection initiation, where it provides protection against host restriction systems. The protein is part of a multicomponent antirestriction system that also includes DarA, DdrA, DdrB, Hdf, and Ulx proteins.

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0006304 DNA modification	IEA GO_REF:0000002	MODIFY	Summary: Too general - DNA modification occurs, but the biological function is specifically antirestriction, not just general DNA modification Proposed replacements: symbiont-mediated evasion of host restriction-modification system Supporting Evidence: PMID:3029954 The darA and darB gene products are found in the phage head and protect any DNA packaged into a phage head, including transduced chromosomal markers, from restriction
GO:0008168 methyltransferase activity	IEA GO_REF:0000043	MODIFY	Summary: Too general - DarB has a methyltransferase domain, but specifically acts on DNA Proposed replacements: DNA-methyltransferase activity Supporting Evidence: GO_REF:0000043 UniProtKB keyword mapping and InterPro domain IPR011639 (Type II methyltransferase M.TaqI-like domain) indicate DNA methyltransferase activity
GO:0032259 methylation	IEA GO_REF:0000043	KEEP AS NON CORE	Summary: Too general and not the core biological process - methylation may occur but the key function is antirestriction defense Reason: While DarB has a methyltransferase domain suggesting methylation activity, the primary biological function is antirestriction. Methylation is a molecular mechanism, not the biological role
GO:0005737 cytoplasm	NAS	NEW	Summary: Added to align core_functions with existing annotations. Reason: Core function term not present in existing_annotations.

Core Functions

Phage-encoded, virion-injected antirestriction factor carrying an N-terminal SAM-dependent DNA-methyltransferase domain (InterPro IPR011639, M.TaqI-like). The DNA-methyltransferase activity is a domain-level bioinformatic inference (GO_REF:0000043); no direct enzymatic methylation has been biochemically demonstrated for DarB. The experimentally supported role is cis-acting protection of virion-packaged DNA against host Type I restriction-modification systems.

Molecular Function:

DNA-methyltransferase activity

Directly Involved In:

symbiont-mediated evasion of host restriction-modification system

Cellular Locations:

cytoplasm

Supporting Evidence:

GO_REF:0000043
UniProtKB keyword mapping and InterPro domain IPR011639 (Type II methyltransferase M.TaqI-like domain) indicate DNA methyltransferase activity
PMID:3029954
The darA and darB gene products are found in the phage head and protect any DNA packaged into a phage head, including transduced chromosomal markers, from restriction

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Gene Description

Existing Annotations Review

Core Functions

References

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