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Restriction enzymes are bacterial enzymes used to cut DNA in a sequence-specific manner. To cleave DNA, they bind to specific palindromic sequences called restriction sites. Such palindromic DNA sequences or inverted repeats are commonly found in regions of functional significance, such as the origin of replication, gene operator sites, and regions containing transcription termination signals.
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The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
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One of the common DNA damages is the chemical alteration of single bases by alkylation, oxidation, or deamination. The altered bases cause mispairing and strand breakage during replication. This type of damage causes minimal change to the DNA double helix structure and can be repaired by the base excision repair (BER) pathways. BER corrects damaged DNA sequences by removing the damaged base and restoring the original base sequence using the complementary strand as a template.
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Single-Molecule Dwell-Time Analysis of Restriction Endonuclease-Mediated DNA Cleavage
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RecA-dependent programmable endonuclease Ref cleaves DNA in two distinct steps.

Erin A Ronayne1, Michael M Cox

  • 1Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.

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|December 28, 2013
PubMed
Summary
This summary is machine-generated.

The bacteriophage P1 Ref protein acts as a RecA-dependent endonuclease, sequentially nicking DNA displacement loops. Its activity on the paired strand is rapid and RecA-independent, while the displaced strand cleavage is slow and RecA-dependent.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Genetics

Background:

  • Bacteriophage P1 recombination enhancement (Ref) protein is a RecA-dependent endonuclease.
  • Ref targets DNA displacement loops formed during homologous recombination.
  • Understanding Ref's mechanism is crucial for DNA repair and genetic engineering applications.

Purpose of the Study:

  • To elucidate the mechanistic details of the Ref protein's endonuclease activity.
  • To investigate the sequential cleavage of DNA strands within displacement loops.
  • To determine the roles of RecA and ATP hydrolysis in Ref-mediated DNA cleavage.

Main Methods:

  • Biochemical assays to analyze Ref protein activity.
  • Site-directed mutagenesis to create Ref active site variants (e.g., H153A).
  • Characterization of cleavage kinetics under varying conditions, including RecA-mediated ATP hydrolysis.

Main Results:

  • Ref acts as a nickase, sequentially cleaving the paired and displaced strands of a DNA displacement loop.
  • Paired strand cleavage is rapid, RecA-independent, and occurs with the Ref H153A variant.
  • Displaced strand cleavage is slow, requires RecA-mediated ATP hydrolysis, and is impaired with Ref H153A.

Conclusions:

  • Ref exhibits distinct mechanisms for cleaving the two DNA strands in a displacement loop.
  • RecA-mediated ATP hydrolysis is essential for the second cleavage event (displaced strand).
  • The findings suggest RecA protein activity limits the overall reaction rate for displaced strand cleavage.