Difference between Type I, Type II and Type III Restriction Endonucleases

Restriction Endonucleases: The Molecular Scissors

These enzymes recognise the base sequence at palindrome sites in DNA duplex and cut its strand. The palindromes in DNA are base pair sequences that are the same when read forward (left to right) or backward (right to left), from a central axis of symmetry. 

EcoR1 found in the colon bacteria Escherichia coli recognises the base sequence GAATTC in DNA duplex and cuts DNA strands between G and A.

There are three main types of restriction endonucleases: Type I, Type II and Type III.

 Difference between Type I, Type II and Type III Restriction Enzymes

Type I

1. Enzyme structure consists of three different subunits.

2. They require ATP, Mg2+ions, S-adenosyl methionine for restriction.

3. They recognise specific sites within DNA but do not cut these sites.

4. They are not used in recombinant DNA technology.

Type II 

1. Enzyme structure is simple

2. They require Mg2+ ions for restriction.

3. They recognise specific sites within the DNA and cut these sites.

4. They are used in recombinant DNA technology.

Type III

1. Enzyme structure consists of two different subunits.

2. They require ATP, Mg2+ions, S-adenosyl methionine for restriction.

3.They recognise specific sites within the DNA but do not cut these sites.

4. They are not used in recombinat DNA technology.