Restriction-modification system evasion by virus

The restriction-modification (RM) system is a defense mechanism present in over 90% of sequenced bacterial and archeal genomes. Its consists of a modification enzyme that methylates a specific DNA sequence in a genome and a restriction endonuclease that cleaves DNA lacking this methylation .<div id="PMID: 11782494" class="hidden">2001 Fred Griffith review lecture. Immigration control of DNA in bacteria: self versus non-self
Noreen E Murray
Microbiology (Reading, Engl.) January 2002; 148: 3?20

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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