Restriction map

A restriction map is a map of known restriction sites within a sequence of DNA. Restriction sites are sites on DNA where restriction enzymes, can cleave the DNA at or near the site. In molecular biology, restriction maps are used as a reference to engineer plasmids or other relatively short pieces of DNA, and sometimes for longer genomic DNA.

Method

There are several valid approaches to construct a restriction map of a DNA sequence. One approach is to sequence the whole molecule and to run the sequence through a computer program that will find the recognition sites that are present for every restriction enzyme known. However, restriction maps are traditionally determined by gel electrophoresis. There are other ways of mapping features on DNA for longer length DNA molecules, such as mapping by transduction.

Before sequencing was automated, it was prohibitively expensive to sequence an entire DNA strand. To find the relative positions of restriction sites on a plasmid, a technique involving single and double restriction digests is used. Based on the sizes of the resultant DNA fragments the positions of the sites can be inferred. Restriction mapping is a very useful technique when used for determining the orientation of an insert in a cloning vector, by mapping the position of an off-center restriction site in the insert.