Methylation of Recognition Sites:
* Restriction enzymes recognize specific DNA sequences called recognition sites. These sites are typically 4-8 base pairs long.
* The cell that produces a restriction enzyme also produces a corresponding methyltransferase enzyme. This enzyme adds a methyl group (CH3) to the recognition site within the bacterial DNA.
* Methylation modifies the recognition site, preventing the restriction enzyme from binding and cutting. This is because the restriction enzyme's active site is specifically designed to recognize and cleave the unmethylated DNA sequence.
Therefore, the cell's own DNA is protected from digestion by its own restriction enzymes due to methylation.
In summary:
1. Restriction enzymes recognize and cut specific DNA sequences.
2. The cell producing the enzyme also produces a methyltransferase that modifies its own DNA at these recognition sites.
3. Methylation prevents the restriction enzyme from binding and cutting the modified DNA.
This mechanism is a crucial part of the bacterial defense system against invading viruses (bacteriophages). By cutting viral DNA while protecting its own, the bacteria can effectively defend itself against viral infection.
