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Related Experiment Videos

A mammalian nicking endonuclease.

M F Lavin, T Kikuchi, C Counsilman

    Biochemistry
    |June 1, 1976
    PubMed
    Summary

    This study purified a calf thymus endonuclease that primarily creates single-strand breaks in double-stranded DNA. The enzyme

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    Area of Science:

    • Molecular Biology
    • Enzymology
    • Biochemistry

    Background:

    • Endonucleases play crucial roles in DNA metabolism and repair.
    • Characterization of novel endonucleases can reveal new insights into DNA processing.
    • Calf thymus is a common source for studying DNA-modifying enzymes.

    Purpose of the Study:

    • To purify and characterize an endonuclease from calf thymus.
    • To investigate the enzyme's substrate specificity and reaction mechanism.
    • To determine the enzyme's biochemical properties, including optimal conditions and molecular weight.

    Main Methods:

    • Purification of endonuclease via chromatography.
    • Enzyme activity assays using double-stranded DNA.
    • Analysis of reaction products using alkaline sucrose density gradients and agarose gel electrophoresis.
    • Determination of molecular weight by gel chromatography.
    • Assessment of inhibition by EDTA and Ca2+.

    Main Results:

    • The purified calf thymus endonuclease primarily induces single-strand breaks in double-stranded DNA.
    • The enzyme shows no activity on denatured DNA and is not inhibited by tRNA.
    • Activity is dependent on bound cations, as indicated by inhibition with EDTA and Ca2+.
    • The enzyme has a broad pH optimum, is inactivated above 45°C, and has a molecular weight of approximately 30,000 Da.
    • Reaction products have an average chain length of 0.8 x 10^6 daltons and generate 3'-hydroxyl and 5'-phosphate ends.

    Conclusions:

    • The characterized calf thymus endonuclease is a novel enzyme with specific DNA-cleaving properties.
    • Its mechanism involves single-strand breaks, suggesting roles beyond DNA restriction.
    • The enzyme's properties indicate a requirement for specific divalent cations for activity.

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