Question

Describe the roles of methylases and restriction enzymes in

eukaryotic & prokaryotic cells.

Answer 1

Restriction enzymes:

• Restriction endonucleases or enzymes (RENs) can act as nuclease that can cut nucleic acid DNA.
• They can cut only at restricted or specific sequences within DNA, hence, these nuclease enzymes are named restriction endonucleases. The recognition sequence comprise of palindromic sequence:

Like for EcoRI – 5’GAATTC3’

                             3’CTTAAG5’

• RENs are produced by prokaryotic bacterial cell to protect them against viruses.
• Not produced by eukaryotes and its effect is prevented by methylation of DNA at various points.
• RENs from different bacteria are used in cloning by inserting REN sites in target DNA. Like EcoRI, BamHI, SalI.

Methylases:

• Methylases are enzymes that add methyl groups.

In prokaryotes:

• Mainly to prevent action of RENs.

Example:

• DAM in E. coli, represents DNA- adenine Methyl transferase. DAM enzyme or DAM methylases (encoded by DAM gene), can transfer methyl group to adenine residues at N-6 position in sequence GATC, from S-adenosylmethionine (SAM).

In Eukaryotes:

• As a part of protection from nucleases, post translational modifications and histone modifications.

Examples:

HMT or or Histone Methyl transferase enzymes- Methylation is associated with constitutive heterochromatin or more tightly coiled chromatin