Host-Controlled Restriction and Modification: Bacterial Defense Mechanism

Host-controlled restriction and modification refer to a set of defense mechanisms employed by bacteria to protect themselves against invading foreign DNA.

Host-controlled restriction involves the use of enzymes known as restriction endonucleases to recognize and cut foreign DNA at specific recognition sites. These enzymes are highly specific and can differentiate between self and non-self DNA based on the presence or absence of specific nucleotide sequences. The result is that foreign DNA is cleaved into smaller fragments that cannot replicate or express genes.

Host-controlled modification involves the addition of chemical modifications to the bacterial DNA at specific recognition sites. These modifications prevent the restriction endonucleases from recognizing and cleaving the bacterial DNA, therefore protecting it from self-digestion.

Together, these mechanisms provide a highly effective defense against foreign DNA, such as that carried by bacteriophages or plasmids. By selectively targeting and destroying foreign DNA while protecting their own, bacteria can maintain the integrity of their genome and preserve their ability to carry out essential cellular functions.