DNA methylase
Meaning of DNA methylase: The enzyme that writes chemical tags onto DNA, and then copies that pattern into every new cell.
Definition of DNA methylase
DNA methylase is an enzyme that attaches a methyl group to DNA, in humans almost always to a cytosine base sitting next to a guanine. The tag does not alter the genetic letter itself; it changes whether that stretch of DNA can be read. Cells use these enzymes both to silence genes and to copy the pattern into daughter cells.
What does the enzyme actually do?
An enzyme is a protein that speeds up a chemical reaction without being consumed by it. This one takes a methyl group, a single carbon atom carrying three hydrogen atoms, from a carrier molecule and fastens it onto a cytosine base. To do that it flips the base out of the double helix into its own active site, adds the tag, and returns the base to position. The sequence of letters is untouched. What changes is the surface that regulatory proteins read when deciding whether to switch the gene on.
What are the different kinds?
| Type | Job |
|---|---|
| Maintenance | Copies the existing pattern onto the new strand after DNA is duplicated |
| De novo | Places tags at sites that carried none before |
The maintenance type is the reason cell identity persists. When DNA is copied, one strand keeps its tags and the new strand has none. The enzyme recognizes that half-tagged state and completes the pattern, so a liver cell divides into two liver cells. The de novo type does the original writing and is most active during early development and in the formation of eggs and sperm.
Why does it matter in cancer?
Tumor cells often show heavy tagging at the control regions of genes that normally restrain growth, silencing them as effectively as deletion would. Because the silencing is chemical, it can be undone. Drugs that block these enzymes are used in some blood disorders and leukemias, working by allowing silenced genes to be read once more. That places DNA methyltransferase, the fuller name for the same enzyme, among the few targets in medicine where the aim is to restore a gene rather than to block a product.
Where else do these enzymes appear?
Bacteria use similar enzymes for an entirely different purpose, tagging their own DNA so that their cutting enzymes treat invading viral DNA as foreign and destroy it. Laboratory work exploits both systems. The bacterial one supplied the tools used to cut and join DNA, and human methylation patterns are now read directly to estimate the age of a tissue sample and to detect tumor DNA circulating in blood.
Also known as
Used in a sentence
Expression of DNA methylase was measured across the tumor samples.
Good to know
A tag added by this enzyme changes whether a gene can be read without altering the sequence, so silencing by methylation is reversible in a way that a deletion is not.