Ocr physically associates with BrxX methyltransferase to neutralizes their ability to both methylate and exclude incoming phage DNA. Ocr structurally mimics the DNA phosphate backbone and interacts directly with EcoKI (both the MTase and REase domain of this type I R–M enzyme), thereby interfering with the activity of this system.
T3 encodes a SAMase that circumvents the SAM-dependent Type I R-M defence of the host E. coli through cleavage of S-adenosyl-methionine (SAM). SAMase also allows T3 to evade BREX defence.
