Restriction Enzyme Analysis,Hexanucleotide,Agarose Gel Electrophoresis,cDNA Clone,Analytical Techniques

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	Restriction Enzyme Analysis - As a restriction enzyme cuts DNA at a specific tetra-, penta-, or hexanucleotide sequence, it is possible to map the position of these particular sequences along the length of a DNA molecule. Digestion with one or more restriction enzymes generates a series of fragments, the size of which can be determined by agarose gel electrophoresis.
The electrophoretic mobility of the fragments can be compared with that of known size markers. From this type of data, a map of restriction sites can be constructed and some information obtained from the restriction map per se. For example, intervening sequences in a gene will mean that two restriction sites in the coding region will be farther apart in a genomic clone than in a cDNA clone. The mRNA precursor to the cDNA clone also does not carry the intervening sequences, so the cDNA clone also will not carry this intron.
Although restriction maps provide some information per se, it is the useful reference points they provide which makes them most valuable. Once the position of these sites is known, the restriction enzymes can be used to cut the DNA specifically for manipulative and analytical procedures. An obvious example of this has already been mentioned: the map of a plasmid allows selection of a suitable site for insertion of foreign DNA. Restriction site information is vital for many other analytical techniques.