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DNA unwinding helicase enzymes are a type of motor protein. Motor proteins can translocate along filaments or polymers using energy generated from ATP hydrolysis. Helicases are involved in all the important cellular processes where DNA unwinding is required, such as DNA replication, repair, recombination, and transcription. They are present in all living organisms, but vary in their structure, function, and mechanism of action. For example, in prokaryotes, DnaB helicase binds and translocates...
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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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DNA replication is carried out by a large complex of proteins that act in a coordinated matter to achieve high-fidelity DNA replication. Together this complex is known as the DNA replication machinery or the replisome.
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Translesion (TLS) polymerases rescue stalled DNA polymerases at sites of damaged bases by replacing the replicative polymerase and installing a nucleotide across the damaged site. Doing so, TLS allows additional time for the cell to repair the damage before resuming regular DNA replication.
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DNA replication is initiated at sites containing predefined DNA sequences known as origins of replication. DNA is unwound at these sites by the minichromosome maintenance (MCM) helicase and other factors such as Cdc45 and the associated GINS complex.The unwound single strands are protected by replication protein A (RPA) until DNA polymerase starts synthesizing DNA at the 5’ end of the strand in the same direction as the replication fork. To prevent the replication fork from falling apart,...
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Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
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The UvrD303 hyper-helicase exhibits increased processivity.

Matthew J Meiners1, Kambiz Tahmaseb1, Steven W Matson2

  • 1From the Department of Biology.

The Journal of Biological Chemistry
|May 7, 2014
PubMed
Summary
This summary is machine-generated.

A mutation in Escherichia coli helicase II (UvrD) enhances its DNA unwinding processivity. This hyper-helicase activity, linked to a more open conformation, may explain its antimutator phenotype.

Keywords:
ATPaseDNA HelicaseDNA Mismatch RepairDNA RepairNucleotide Excision RepairProcessivityProtein-Protein Interaction

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Genetics

Background:

  • DNA helicases are crucial enzymes that unwind double-stranded DNA using ATP hydrolysis.
  • Escherichia coli helicase II (UvrD) plays vital roles in DNA replication, repair, and recombination pathways.
  • A specific UvrD mutation (uvrD303) at residues 403-404 results in antimutator and UV-sensitive phenotypes.

Purpose of the Study:

  • To investigate the molecular mechanism underlying the enhanced helicase activity of the UvrD303 mutant.
  • To determine how the 2-amino acid substitution affects the protein's unwinding processivity and conformation.

Main Methods:

  • Purification of the UvrD303 mutant protein.
  • In vitro helicase activity assays.
  • Rapid quench, pre-steady state kinetic experiments to analyze unwinding kinetics.

Main Results:

  • The UvrD303 mutant exhibits significantly increased DNA unwinding activity compared to the wild-type.
  • Kinetic analysis reveals that the enhanced activity is due to increased processivity of the unwinding reaction.
  • The mutation likely weakens the interaction between the 2B and 1B subdomains, leading to a more open conformation.

Conclusions:

  • The UvrD303 mutation enhances DNA unwinding processivity, potentially via a strand displacement mechanism.
  • The 2B subdomain appears to have an autoregulatory role in UvrD function.
  • Increased unwinding processivity of UvrD303 may directly contribute to its antimutator phenotype.