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Related Concept Videos

DNA Topoisomerases02:02

DNA Topoisomerases

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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.
Types and Mechanism of action
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An organism’s genome needs to be duplicated in an efficient and error-free manner for its growth and survival. The replication fork is a Y-shaped active region where two strands of DNA are separated and replicated continuously. The coupling of DNA unzipping and complementary strand synthesis is a characteristic feature of a replication fork.   Organisms with small circular DNA, such as E. coli, often have a single origin of replication; therefore, they have only two replication...
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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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Single-Strand DNA Binding Proteins01:03

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For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes...
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DNA Helicases00:55

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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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Condensins are large protein complexes that use ATP to fuel the assembly of chromosomes during mitosis. They transform the tangled, shapeless mass of post-interphase DNA into individualized chromosomes by compacting, organizing, and segregating chromosomal DNA.
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Studying DNA Looping by Single-Molecule FRET
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Condensin-driven loop extrusion on supercoiled DNA.

Eugene Kim1,2, Alejandro Martin Gonzalez1, Biswajit Pradhan1,2

  • 1Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, Netherlands.

Nature Structural & Molecular Biology
|July 14, 2022
PubMed
Summary
This summary is machine-generated.

Condensin (SMC complex) uses DNA supercoiling to enhance its loop extrusion, forming stable, supercoiled DNA loops. This reveals how DNA topology influences chromosome organization by molecular motor proteins.

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Area of Science:

  • Molecular Biology
  • Chromatin Structure
  • Biophysics

Background:

  • Condensin, a Structural Maintenance of Chromosomes (SMC) complex, functions as a molecular motor.
  • It organizes chromosomes via DNA loop extrusion, a process potentially hindered by torsional stresses.
  • The impact of DNA supercoiling on loop extrusion remained unclear.

Purpose of the Study:

  • To investigate how DNA supercoiling influences condensin-driven DNA loop extrusion.
  • To elucidate the mechanism of condensin's interaction with supercoiled DNA.
  • To understand the role of DNA topology in SMC complex function.

Main Methods:

  • Time-lapse single-molecule imaging of condensin on supercoiled DNA.
  • Atomic force microscopy (AFM) to visualize DNA structures and condensin activity.
  • Biophysical analysis of DNA loop formation and supercoil generation.

Main Results:

  • Positively supercoiled DNA stimulates condensin binding and DNA looping.
  • Condensin preferentially binds to the tips of supercoiled plectonemes.
  • Condensin collects plectonemes into stable, supercoiled loops and generates supercoils in an ATP-dependent manner.

Conclusions:

  • DNA supercoiling positively regulates condensin's loading and loop extrusion activity.
  • Condensin actively generates supercoils during loop formation, creating highly stable structures.
  • This study clarifies the interplay between DNA topology and SMC complex-mediated chromosome organization.