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 (tetraschizomers or hexaschizomers,
"four-cutters" or "six-cutters"). Some have
10 bp 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",
"Doc: note, I dissent. A fast never prevents a fatness.
I diet on cod". The one-word record holder is the
15-letter 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.
Table © 2000 by
Griffiths et al. ; text © 2024 by Steven M. Carr