Some RM systems (restriction-modification systems) are plasmid-borne and are transferred through bacterial conjugation. As you all know, there are two genes in an RM system, the gene that codes for the restriction enzyme that restricts a certain nucleotide sequence and the other that codes for the methyltransferase that methylate the sequence to protect the cell from its own restriction enzymes. If these genes are both being expressed at the same rate after the bacteria receives this plasmid, how is the bacteria's DNA protected from the restriction enzymes for the first few hours of expression if the methyltransferase have not yet methylated the entire host genome yet?

Thank you,


  • $\begingroup$ About which systems are you talking? CrispR? LoxP? $\endgroup$
    – Chris
    Mar 9, 2015 at 18:53
  • $\begingroup$ Is it different from one system to another? My main focus would probably be type II, but beyond that it doesn't really matter, any system you choose to answer for would be fine. $\endgroup$
    – CDB
    Mar 9, 2015 at 19:03
  • $\begingroup$ So you're asking about what happens when bacteria are simultaneously transformed with a gene for a restriction enzyme that cuts at unmethylated site X, AND an enzyme that methylates site X? $\endgroup$
    – user137
    Mar 9, 2015 at 20:04
  • $\begingroup$ In essence yes. I'm wondering how the cell protects its own DNA from the restriction enzymes until the methyltransferase methylate the DNA. $\endgroup$
    – CDB
    Mar 9, 2015 at 20:34
  • 2
    $\begingroup$ I don't really know, but I assume it comes down to how quickly each protein is expressed, how quickly each enzyme catalyzes its reaction, and how well a cell repairs it genome. With a large population of transformed cells, I assume some will be methylated before they are cut, and survive. If methylation can be passed down from generation to generation, those will be selected. But again, I barely know anything about DNA methylation. $\endgroup$
    – user137
    Mar 9, 2015 at 21:31


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