Module 2 : ENZYMES IN GENETIC ENGINEERING

Lecture 3 : Enzymes in Modification- Phosphatases and Methylases and their Mechanism of Action


Methyltransferase can be classified in three groups:

a) m6A-generates N6 methyladenosine,

b) m4C-generates N4 methylcytosine,

c) m5C-generatesN5 methylcytosine.

m6A and m4C methyltransferase are primarily found in prokaryotes. These enzymes are responsible for methylation of DNA sequences in order to prevent the host from digesting its own genome via its restriction enzyme.

Fig 2-3.2: Activity of restriction and methylase enzymes

Restriction enzyme EcoR I cleaves within the recognition sequence if the DNA is unmethylated. On methylation by methylases, the restriction enzyme EcoR I is inhibited from cleaving within the restriction site.

Some common examples of methytransferases are: DNA adenyl methytransferase (DAM), histone methyltransferase, O-methyltransferase etc. DAM methylase is generally used in recombinant DNA technology which can methylate adenine (A) in the sequence 5'GATC3'. This enzyme can methylate a newly synthesized DNA strand on specific sites.