Sequence-specific double-strand cuts

Restriction enzymes are named after the bacterium from which they are isolated. For example, EcoRI is from Escherichia coli, and BamEII is from Bacillus amyloliquefaciens (Table 40-2). The first three letters in the restriction enzyme name consist of the first letter of the genus (E) and the first two letters of the species (co). These may be followed by a strain designation (R) and a roman numeral (I) to indicate the order of discov-ery (eg, EcoRI, EcoRIE). Each enzyme recognizes and cleaves a specific double-stranded DNA sequence that is 4—7 bp long. These DNA cuts result in blunt ends (eg,... 

Restriction enzymes are sequence-specific endonucleases that cut double-stranded DNA at specific sites. 

Type II restriction endonucleases (25) are enzymes isolated from procaryotes which recognize and make double-stranded cuts at specific DNA sequences. We investigated how platination of plasmid pBR322 would affect the ability of the enzyme Bam HI to cut at its single recognition sequence in this plasmid (23) Bam HI... 

Partial digestion by DNAase-I is widely used in the study of chromatin structure. Micrococcal nuclease (also called Staphyloccocal nuclease) makes double-stranded cuts initially in the linker DNA between nucleosomes, useful for mapping the positions of nucleosomes. Micrococcal nuclease digests must be interpreted carefully because this nuclease shows some sequence specificity when partial digestion of purified DNA is carried out as a control. In addition to these enzyme probes, there are chemical reagents that cut DNA. These reagents are much less sequence-dependent than even DNAase-I. Accessible DNA can also be labeled by methylating enzymes. 

Double stranded DNA can be enzymatically cleaved by commercially available endonucleases (restriction enzymes). These enzymes recognise specific, usually palindromic, sequences and cut specifically at those positions. 

The most striking specificity in DNA hydrolysis is displayed by the restriction endonucleases which are discussed further in Chapter 26. These fussy catalysts cleave only at points within or close to a defined sequence of several nucleotides in double-stranded DNA. For example, the enzyme EcoR I cuts only at the following palindromic sequence ... 

Attempts are being made to design semisynthetic restriction endonucleases specific for single-stranded DNA or RNA. For example, an oligonucleotide with a sequence complementary to a sequence adjacent the linkage that is to be cut can be covalently linked to a relatively nonspecific nuclease. Such an enzyme derived from micrococal nuclease cuts a single-stranded chain of either DNA or RNA adjacent to the double-stranded region of the ES complex.839... 

Restriaion enzymes are a revolutionary class of proteins discovered in prokaryotic organisms in the early 1970s (1-5). These enzymes reproducibly cut within double-stranded DNA molecules at specific nucleotide recognition sequences, termed restriction sites, hence their more specific appellation as restriction endonucleases (Fig. 1). Their complete range of enzymatic functions is not fully... 

One of the most important developments in the recent history of biochemistry is the discovery of restriction endonucleases (also called restriction enzymes). Restriction endonucleases are enzymes that catalyze the double-strand cleavage of DNA at specific base sequences. That is, restriction enzymes cut DNA strands at specific DNA sequences, generating fragments of specific sizes that can be separated and visualized on gel electrophoresis (Figure 25.6). 

Restriction enzyme An enzyme that cuts long double-stranded DNA chains only occasionally, where it finds a specific sequence of nucleotide bases. Physiologically a defence against foreign DNA scientifically a tool for molecular genetics. 

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