Restriction sites
Encyclopedia
Restriction sites, or restriction recognition sites, are locations on a DNA
molecule containing specific (4-8 base pairs in length)sequences of nucleotide
s, which are recognized by restriction enzyme
s. These are generally palindromic sequence
s (because restriction enzymes usually bind as homodimers), and a particular restriction enzyme may cut the sequence between two nucleotides within its recognition site, or somewhere nearby. For example, the common restriction enzyme EcoRI
recognizes the palindromic sequence GAATTC and cuts between the G and the A on both the top and bottom strands, leaving an overhang (an end-portion of a DNA
strand with no attached complement) on each end, of AATT. This overhang can then be used to ligate in (see DNA ligase
) a piece of DNA with a complementary overhang (another EcoRI-cut piece, for example).
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
molecule containing specific (4-8 base pairs in length)sequences of nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
s, which are recognized by restriction enzyme
Restriction enzyme
A Restriction Enzyme is an enzyme that cuts double-stranded DNA at specific recognition nucleotide sequences known as restriction sites. Such enzymes, found in bacteria and archaea, are thought to have evolved to provide a defense mechanism against invading viruses...
s. These are generally palindromic sequence
Palindromic sequence
A palindromic sequence is a nucleic acid sequence that is the same whether read 5' to 3' on one strand or 5' to 3' on the complementary strand with which it forms a double helix....
s (because restriction enzymes usually bind as homodimers), and a particular restriction enzyme may cut the sequence between two nucleotides within its recognition site, or somewhere nearby. For example, the common restriction enzyme EcoRI
EcoRI
EcoRI is an endonuclease enzyme isolated from strains of E. coli, and is part of the restriction modification system.In molecular biology it is used as a restriction enzyme. It creates sticky ends with 5' end overhangs...
recognizes the palindromic sequence GAATTC and cuts between the G and the A on both the top and bottom strands, leaving an overhang (an end-portion of a DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
strand with no attached complement) on each end, of AATT. This overhang can then be used to ligate in (see DNA ligase
DNA ligase
In molecular biology, DNA ligase is a specific type of enzyme, a ligase, that repairs single-stranded discontinuities in double stranded DNA molecules, in simple words strands that have double-strand break . Purified DNA ligase is used in gene cloning to join DNA molecules together...
) a piece of DNA with a complementary overhang (another EcoRI-cut piece, for example).