Restriction enzymes: Types and nomenclature.

1. Restriction Enzymes
For B.Sc III(Semester VI)
(As per the syllabus of S.G.B.A.U.
Amravati)
By : Mohanish V. Wankhade
M.Sc.(Botany),CSIR-NET,SET,GATE

2. Restriction Enzymes
• These are the molecular scissors , which cut the
DNA at specific site.
•Different types of Restriction enzymes have
different recognition sequence.
•On the basis of nature of digestion of DNA,
restriction enzyme may be exonuclease or
endonuclease.
Restriction exonucleases:
These are the enzymes which cut the
DNA outer side and produces blunt ends.
Restriction Endonuclease: These are enzymes which
cut the DNA inner side and produces sticky ends.

3. By the mode of action, there are three types of
restriction endonucleases viz. Type I, Type II and Type
III.
Type I R.E.
• Type I restriction enzymes such as Eco B, Eco K.
• They function simultaneously as an endonuclease and
methylase(modification)
• They move along with DNA in a reaction and require
Mg2+,S-adenosyl methionine and ATP as cofactors.
•These enzymes shows specificity for recognition site
but not for cleavage.
•Restriction site is 15bp long and cleavage site is about
1000 bp away from 5′ end of recognition.

4. 5′ AAA*CNNNNNNNNNG TCGC 3′
3 ′TTT GNNNNNNNNNC*AGCG 5′
N-unspecific base
Type II R.E.
•This enzyme first isolated by Hamilton smith.
•These enzymes have separate activity for cleavage
and methylase
•These are most stable enzymes that require Mg2+
as a cofactor.
•Important one which used in gene manipulation.
•The first Type II R.E. is Eco RI.
•Recognition site is palindromic sequence ( A
nucleotide sequence that are the same when read

5. from left to right or vice-versa.
Some examples of Type II R.E. are-
Micro-organism R.E. Cleavage site
Bacillus amyloliqufacience Bam HI 5′ G*GATCC 3′
3′ CCTAG*G 5′
Haemophilus influenzae Hind III 5′GTpy*puAC 3′
3′CApu*pyTG5′
Providentia sturtii Pst I 5′CTGCA*G 3′
3′G*ACGTC5′

6. Type III R.E.
•Type III restriction endonucleases made up of two
subunits.
•one specifies for site recognition and modification.
Other for cleavage.
•It require Mg2+,ATP as a cofactors.
•Some examples of Type III R.E. are Hpa I, Mbo II, Fok
I etc.
•They have 5-7 bp symmetrical recognition site and
cleaves DNA at specific site in a non-palindromic
sequence.

7. Nomenclature Of Restriction Enzymes
The restriction enzymes are named based on
some of the following principles
• Name of the organism from which enzyme is isolated
is identified by the first letter of genus name and the first
two letters of species name to form a three letter
abbreviation in italic.
•First letter is capital and other two are small e.g Eco
from Escherichia coli.
•A strain is identified is written as subscript e.g. Eco R
for E.coli RY strain.
•When a strain has several restriction site they are
identifies as roman numerical e.g. Eco RI, Eco RII.