Endonuclease Deoxyribonuclease

Restriction endonuclease A deoxyribonuclease which cuts DNA at specific sequences which exhibit twofold symmetry about a point. Name derives from the fact that their presence in a bacterial cell prevents (restricts) the growth of many infecting bacteriophages. 

Site-specific deoxyribonuclease (type 11)— restriction endonuclease ... 

Deoxyribonuclease IV (phage T4-induced) [EC 3.1.21.2], also called endodeoxyribonuclease IV (phage T4-induced) and endonuclease IV, catalyzes the endonucleolytic cleavage of DNA, preferring single-stranded, to 5 -phosphooligonucleotide end products. 

All of the bacterial deoxyribonucleases that have been examined in detail possess a specificity directed in varying degrees toward the secondary structure of the polydeoxynucleotide. With one recent exception, none of the deoxyribonucleases shows a simple base specificity whereby they attack phosphodiester bonds adjacent to a single base. However, it is now clear that several of the endonucleases may possess an extremely high order of specificity and have the capacity to recognize and attack one or a few phosphodiester bonds in polydeoxynucleotide chains composed of many thousands of internucleotide linkages. 

The existence of a deoxyribonuclease in E. coli bound to an inhibitory RNA was first suggested by Kozloff (3< ) who found that the DNase activity of freshly prepared extracts could be markedly enhanced by pretreatment with ribonuclease. The enzyme was subsequently purified and freed of inhibitor (39). The purified enzyme termed endonuclease I could, in turn, be competitively inhibited by a variety of RNA s including transfer RNA, and Ri values as low as 10-8 M (nucleotide) have been observed (40). Examination of various purified RNA species and synthetic polyribonucleotides for their inhibitory activity has led... 

A deoxyribonuclease termed streptodornase, optimally active at pH 7.0 in the presence of magnesium ion, has been partially purified from culture fluids of Streptococcus pyogenes (45). This enzyme yields a distribution of products from DNA very similar to that seen with E. coli endonuclease I Only traces of mono- and dinucleotides are found, the majority of products being rather large oligonucleotides terminated by... 

Barry, M.A. and Eastman, A. (1993) Identification of deoxyribonuclease II as an endonuclease involved in apoptosis. Arch, Biochem. Biophys., 300, 44CMI50. 

The involvement of CAD as the endonuclease in apoptosis contradicts previous suggestions of other endonucleases involved in apoptosis. CAD is a Ca2+-independent endonuclease whereas many groups have implicated a Ca2+-dependent endonuclease in apoptosis [65-69], However, we have presented considerable evidence that Ca2+ is not required for DNA digestion, and furthermore, that depleting Ca2+ is a stimulus for DNA digestion [70][71], We have implicated deoxyribonuclease II (DNase II) as an alternate endonuclease involved in apoptosis [72], DNase II requires low pH for activity, and we have established that intracellular acidification is a common occurrence in apoptosis [73-76]. Intracellular acidification is a conse-... 

DNase. Deoxyribonuclease, a class of enzymes that digest DNA. The most common is DNase I, an endonuclease that digests both single and double-stranded DNA. 

A variety of enzymes break phosphodiester bonds in nucleic acids deoxyribonucleases (DNases) cleave DNA and ribonucleases (RNases) cleave RNA. DNases usually are specific for single- or double-stranded DNA although some DNases can cleave both. DNases can act as exonucleases in which they remove one nucleotide at a time from either the 3 or 5 end of the strand. Other DNases function as endonucleases and are specific for cleaving between particular pairs of bases. 

The role of the divalent metal ions present in natural phosphodiesterases became clear in bovine pancreatic deoxyribonuclease I (DNase I), the first endonuclease structure determined by X-ray crystallography. The nucleophilic attack of a water molecule activated by a histidine residue is facilitated by the interaction of a calcium ion with the phosphate group to be cleaved (291). Glutamic and aspartic residues involved in magnesium binding have been identified in the crystal structure of four type II restriction enzymes EcoRl (292), EcoRV (293), Pvull (294), and BamHl (295), as well as in that of the repair... 

Nucleases a group of hydrolytic enzymes which cleave nucleic acids. Exonucleases attack the nucleic acid molecule at its terminus, whereas endonucleases are able to catalyse a hydrolytic cleavage within the polynucleotide chain. Deoxyribonucleases (DNAases) are specific for DNA, ribonucleases (RNAases) for RNA. All N. are Phosphodiesterases (see) they catalyse the hydrolysis of either the 3 or 5 bond of the 3, 5 -phosphodiester linkage. Ribonuclease (see) has been extensively studied. 

Phosphodiesterases enzymes that catalyse the hydrolytic deavage of phosphodiesters, e.g. endonucleases, Ribonuclease (see) and Deoxyribonuclease (see), and the less specific exonucleases. The latter... 

Bovine pancreatic deoxyribonuclease (DNase I) is an endonuclease that cleaves both ssDNA and dsDNA to produce primarily 5 -P dinucleotides and 5 -P oligonucleotides (Fig. 3.1). DNase I degrades dsDNA in a sequence-nonspecific manner. The enzyme requires divalent cations (both Ca and Mg or Mn ) as cofactors for full double-strand cutting activity. In the presence of Mg alone as a cofactor, DNase I exhibits nicking activity and the single-strand nucleolytic activity is more discriminatory. 

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