Nucleases

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Nucleases are a group of enzymes whose main function is the partial or complete breakdown of nucleic acids . One also speaks of partial or complete digestion of a substrate .

Classification criteria

There are various properties of nucleases that sometimes serve as criteria for their classification:

  • Type of the primarily digested nucleic acid type: RNA ( ribonucleases , RNases for short), DNA ( deoxyribonucleases , DNases for short).
  • Type of secondary structure of the substrate: single strands, double strands, single strands and double strands.
  • Type of digestion: breakdown from the end ( exonucleases ), internal cut ( endonucleases ), external breakdown and internal cuts.
  • Place of attack in the sugar-phosphate framework: between phosphate and 5'-site of (deoxy) ribose, between phosphate and 3'-site of (deoxy) ribose.
  • Role of a certain base sequence: sequence-specific, sequence-unspecific.
  • Origin: naturally occurring nucleases, recombinant nucleases (produced by genetic engineering).

Usually nucleases are named after their origin. For this purpose, the naturally occurring nucleases are often named after the type of organism from which they come and numbered in the order of their isolation and characterization. So Eco RI which I restriction endonuclease from the bacterial strain " Escherichia coli R".

The classification according to various criteria does not claim to be complete, as finer classifications exist and many nucleases do not have any clearly assignable properties. A finer classification is made e.g. B. towards the exonucleases, which are based on the direction of digestion and have no relevance for endonucleases (5'-3 'and 3'-5' exonucleases). The sequence-specific double-stranded restriction endonucleases (also called restriction enzymes) are in turn classified into types I to IV depending on the relationship between the binding and cleavage sites.

Systematics

According to the enzyme classification system of the Nomenclature Committee of the International Association for Biochemistry and Molecular Biology ( NC-IUBMB ), the vast majority of nucleases are hydrolases (EC 3) that act on ester bonds (EC 3.1). The esterases that digest nucleic acids are summarized there in the groups EC 3.1.11 to EC 3.1.31.

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