How does methylation of DNA occur and what does it do to protect DNA from being cleaved?
Belen Hurle, Ph.D.: Methyl group tags in the DNA of humans and other mammals play an important role in determining whether some genes are or are not expressed. Genes unnecessary for any given cell’s function can be tagged with the methyl groups. Simpler organisms, such as many types of bacteria and the single-celled yeast, usually do not use methyl group tagged C’s in regulating their genes. Some bacteria, but not all, use methyl group tagged A’s (mA) for this purpose. However, most bacteria have specific patterns of mC and mA in their DNA as a signal that says “this is my DNA” and acts as part of an immunity mechanism that allows bacteria to destroy the DNA from infecting viruses without destroying their own DNA. In other words, the distinction between “foreign” and “self” DNA is made through a specific methylation of the bacterial DNA, which protects it from cleavage by the restriction enzymes. The viral DNA, which is not protected, is quickly degraded by the restriction enzymes carr
