Nuclease(redirected from Exonucleases)
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a phosphodiesterase enzyme that splits nucleic acids into mononucleotides and oligonucleotides.
Nucleases are widely distributed in the cells of microorganisms, plants, and animals. These enzymes are especially abundant in pancreatic juice and in the saliva of mammals and man. A distinction is made between 3′ and 5′ nucleases, depending on whether the enzyme splits the phosphodiester bonds of the nucleic acid to form nucleotides that contain phosphoric acid residues on the 3’- or 5’-carbon of the carbohydrate fragment. The terminal mononucleotides are separated by exonucleases; nucleases that split bonds within the polynucleotide chain are called endonucleases. Ribonucleases and deoxyribonucleases are distinguished according to whether they split ribonucleic or deoxyribonucleic acids. Nonspecific nucleases are able to split chains of both types of acids.
Nucleases are proteins—usually basic—with a comparatively low molecular weight; for example, the pancreatic ribonuclease molecule consists of 124 amino-acid residues. The biological function of nucleases is to digest and split nucleic acids that are foreign to the organism, for example, nucleic acids of invasive viruses. This is the rationale for using nucleases to treat certain viral diseases. Nucleases participate in the repair of deoxyribonucleic acid (DNA) by eliminating the fragmented portions of the DNA molecule from the polynucleotide chain. Nucleases also appear to play a major role in regulating the synthesis and decomposition of nucleic acids in cells. A nuclease enzyme can be used in laboratories to free preparations from a specific nucleic acid, to determine the structure of nucleic acids, and to study the mechanism of nucleic acid decomposition and synthesis.
REFERENCEShapot, V. S. Nukleazy. Moscow, 1968.
I. B. ZBARSKII