Restriction Map

Restriction Map

1696 R e s t r i c t i o n F r a g m e n t L e n g t h Po l y m o r p h i s m ( R F L P ) more strongly to their recognition sites than any other se...

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1696

R e s t r i c t i o n F r a g m e n t L e n g t h Po l y m o r p h i s m ( R F L P )

more strongly to their recognition sites than any other sequences (some binding energy may be lost due to DNA distortion). In contrast, EcoRV-like enzymes bind every DNA sequence equally well, including their own recognition sites; no discrimination between sites can occur at the level of DNA binding. Instead, discrimination arises at the catalytic step; only the DNA in the specific complex is sufficiently distorted to allow Mg2‡ ions to bind and so facilitate cleavage (the Mg2‡ ions associate weakly when the enzyme is bound at any other site). The structure of the DNA in the protein±DNA complex is different in each case. With EcoRV the DNA is severely distorted, whereas with BamHI it is essentially B-DNA like. Despite the differences between and within the groups, the active site regions of all the enzymes are similar. It is not yet clear if this relates to a shared mechanism for the actual DNA cleavage step.

Restriction Map

Further Reading

The RET (Rearranged in Transfection) protooncogene encodes a cell surface receptor tyrosine kinase which is required for development of the kidney and some nerves. RET is frequently rearranged in papillary thyroid carcinoma, resulting in fusion of the RET tyrosine kinase domain to sequences of one of several other proteins. These chimeric proteins are able to dimerize and stimulate cell proliferation and tumor formation in the absence of the signals that normally control RET activation. Inherited point mutations in RET, which also activate the protein inappropriately, cause the cancer syndrome multiple endocrine neoplasia type 2 (MEN 2). Conversely, mutations that inactivate RET are found in patients with the birth defect Hirschsprung disease, which is characterized by absence of the nerves and ganglia of the lower intestine.

Roberts RJ and Macelis D (1998) REBASE ± Restriction enzymes and methylases. Nucleic Acids Research 26: 338±350 (http://www.neb.com/rebase/) Roberts RJ and Macelis D (2001) REBASE ± Restriction enzymes and methylases. Nucleic Acids Research 29: 268±269 (http://rebase.neb.com)

See also: DNA Cloning; DNA Mapping; DNA Modification; Nuclease; Recombinant DNA Technology; Restriction and Modification

Restriction Fragment Length Polymorphism (RFLP) L Silver Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.1119

A restriction fragment length polymorphism (RFLP) is a DNA variation that affects the distance between restriction sites (most often by a nucleotide change that creates or eliminates a site) within or flanking a DNA fragment recognized by a cloned probe. RFLPs are detected as bands of different sizes on Southern blot hybridization. The term RFLP is commonly used even in situations where the DNA variation may not represent a true polymorphism in the populationbased definition of this term. See also: Restriction Endonuclease

Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.2003

A restriction map is a map of DNA illustrating the position of sites recognized and cleaved by various restriction endonucleases. See also: Restriction Endonuclease

RET Proto-Oncogene L M Mulligan Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.1614

See also: Hirschsprung's Disease; Multiple Endocrine Neoplasia

Reticulation W Fitch Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.1486

Mathematically, a tree is a graph for a minimally connected set of points (nodes) connected by edges (branches). Minimally connected means that, for any pair of points in the graph, there is one and only one path that gets you from one node to another node. If there were more than one way of getting from one