Some examples of Type II restriction
endonucleases
Restriction endonucleases
are
used by bacteria to recognize foreign DNA
and destroy (restrict) it by introducing
double-stranded cuts at
characteristic recognition
sites. They are typically named after the bacterial
species from
which they were first isolated. For example, EcoRI was the (I)st (R)estriction endonuclease isolated
from E.
coli: Eco + R + I. Most endonucleases used in
molecular
biology recognize four or
six base
sites ("four-cutters"
and "six-cutters");
some have
ten-base sites, and are called "long
cutters" because the interval between sites is much
greater.
Restriction sites are molecular palindromes.
A palindrome is a word
or phrase that reads the same
forward or backward: "Able was I ere I saw Elba",
"Madame I'm Adam," or
the Finnish word for a soap seller, "Saippuakauppias". DNA
palindromes read
the same forward and backward when both strands are
considered. In the
first example above, the recognition site of EcoRI
is 5'-GAATTC-3', so
the paired
strand is 3'-CTTAAG-5':
the
double-stranded 6 bp sequence will therefore read the same in
either
direction.
Figure © 2000
by
Griffiths
et
al. ; text © 2012 by Steven
M.
Carr