Restriction-modification system evasion by virus (kw:KW-1258)

Bacterial viruses have evolved different strategies to evade the restriction-modification system . Some viruses encode their own methyltransferase in order to protect their genome from host restriction enzymes . Instead, bacteriophage T7 encodes the OCR protein that blocks the active site of several restriction enzymes by mimicking the phosphate backbone of B-form DNA. Other bacterial viruses use unusual bases on their genome to avoid restriction. Bacteriophages SPO1, SP82, and 2C replace thymidine with 5-hydroxymethyluracil while phages PBS1 and PBS2 thymine is completely changed to uracil.

Family	Genus	Virus	Strategy of RM evasion	Viral protein	Ref.
Siphoviridae	Tunalikevirus	Bacteriophage T1	Viral methyltransferase	Dmt methyltransferase
Podoviridae	T7likevirus	Bacteriophage T3	Viral SAMase	S-adenosyl-L-methionine hydrolase
Myoviridae	T4likevirus	Bacteriophage T4	Viral methyltransferase	Dam methyltransferase
Myoviridae	T4likevirus	Bacteriophage T2	Viral methyltransferase	Dam methyltransferase
Podoviridae	T7likevirus	Bacteriophage T7	Inhibition of type-I RM enzymes	OCR protein
Myoviridae	Punalikevirus	Bacteriophage P1	Internal capsid protein	DarA, DarB
Podoviridae	P22likevirus	Bacteriophage P22	Modification of host methylase activity	Ral
Siphoviridae	Lambdalikevirus	Bacteriophage λ reverse	Modification of host methylase activity	Lar
Siphoviridae	Lambdalikevirus	Bacteriophage λ	Modification of host methylase activity	Ral
Myoviridae	Mulikevirus	Bacteriophage Mu	Adenine acetyltransferase	Mom