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Related Experiment Videos

Sequence-specific DNA recognition by the SmaI endonuclease

B E Withers1, J C Dunbar

  • 1Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan 48201.

The Journal of Biological Chemistry
|March 24, 1995
PubMed
Summary
This summary is machine-generated.

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SmaI endonuclease binds DNA specifically without magnesium, with affinity increasing for longer DNA fragments. This enzyme

Area of Science:

  • Molecular Biology
  • Enzymology
  • Biochemistry

Background:

  • SmaI endonuclease is a restriction enzyme that recognizes and cleaves specific DNA sequences.
  • Understanding the binding and catalytic mechanisms of restriction enzymes is crucial in molecular biology.

Purpose of the Study:

  • To investigate the DNA binding properties of SmaI endonuclease.
  • To elucidate the role of magnesium in SmaI binding and catalysis.
  • To determine the interaction sites between SmaI and its DNA substrate.

Main Methods:

  • Equilibrium binding assays were used to determine the association constant (KA) of SmaI for DNA.
  • Kinetic assays were performed to estimate the Michaelis constant (Km).
  • Footprinting analyses (dimethyl sulfate and missing nucleoside) and ethylation interference assays were employed to identify protein-DNA contact points.

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Main Results:

  • SmaI specifically binds to DNA in the absence of magnesium, with a KA of 0.9 x 10(8) M-1 for a 22-base duplex.
  • SmaI affinity increases with DNA length, showing a KA of 1.2 x 10(9) M-1 for a 195-base pair fragment.
  • The enzyme interacts with each base pair in the recognition sequence and contacts three adjacent phosphates on each DNA strand.
  • A predicted contact with the phosphate 3' of the scissile bond may be involved in catalysis.

Conclusions:

  • SmaI exhibits specific DNA binding independent of magnesium, with enhanced affinity for longer DNA substrates.
  • Detailed analysis of protein-DNA interactions provides insights into the SmaI recognition and cleavage mechanism.
  • The findings suggest a potential role for a specific phosphate contact in the catalytic mechanism of SmaI endonuclease.