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Related Concept Videos

Spreading of Chromatin Modifications02:25

Spreading of Chromatin Modifications

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The histone proteins in the nucleosomes are post-translationally modified (PTM) to increase or decrease access to DNA. The commonly observed PTMs are methylation, acetylation, phosphorylation, and ubiquitination of lysine amino acids in the histone H3 tail region. These histone modifications have specific meaning for the cell. Hence, they are called "histone code". The protein complex involved in histone modification is termed as "reader-writer" complex.
Writers
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Chromatin Modification in iPS Cells01:32

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Chromatin modification alters gene expression; therefore, scientists can add histone-modifying enzymes, histone variants, and chromatin remodeling complexes to somatic cells to aid reprogramming into pluripotent stem (iPS) cells.
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In eukaryotic cells, nascent mRNA transcripts need to undergo many post-transcriptional modifications to reach the cell cytoplasm and translate into functional proteins. For a long time, transcription and pre-mRNA processing were considered two independent events that occur sequentially in the cell. However, it has now been well established that transcription and pre-mRNA processing are two simultaneous processes that are precisely regulated inside the cell.
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Duplication of Chromatin Structure02:05

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The process of chromosome duplication during cell division requires genome-wide disruption and re-assembly of chromatin. The chromatin structure must be accurately inherited, reassembled, and maintained in the daughter cells to ensure lineage propagation.
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Heterochromatin02:38

Heterochromatin

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The extent of chromatin compaction can be studied by staining chromatin using specific DNA binding dyes. Under the microscope, the dense-compacted regions that take up more dye are called heterochromatin. Heterochromatin is further classified into two forms – constitutive heterochromatin and facultative heterochromatin.
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Nucleosome Remodeling

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Nucleosomes are the basic units of chromatin compaction. Each nucleosome consists of the DNA bound tightly around a histone core, which makes the DNA inaccessible to DNA binding proteins such as DNA polymerase and RNA polymerase. Hence, the fundamental problem is to ensure access to DNA when appropriate, despite the compact and protective chromatin structure.
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Related Experiment Video

Updated: Jul 12, 2025

Repressing Gene Transcription by Redirecting Cellular Machinery with Chemical Epigenetic Modifiers
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Repressing Gene Transcription by Redirecting Cellular Machinery with Chemical Epigenetic Modifiers

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Chromatinization Modulates Topoisomerase II Processivity.

Jaeyoon Lee1, Meiling Wu1,2, James T Inman1,2

  • 1Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA.

Biorxiv : the Preprint Server for Biology
|October 24, 2023
PubMed
Summary
This summary is machine-generated.

Type IIA topoisomerases (topo II) efficiently relax DNA supercoiling. Chromatin significantly enhances topo II processivity, even under low torsional stress, revealing its crucial role in DNA management.

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Related Experiment Videos

Last Updated: Jul 12, 2025

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Genetics

Background:

  • Type IIA topoisomerases are vital enzymes for managing DNA torsional stress in vivo.
  • The precise mechanisms by which DNA supercoiling influences topoisomerase II (topo II) activity are not fully understood.

Approach:

  • Utilized single-molecule techniques to investigate the effects of DNA torsion on supercoiling relaxation by eukaryotic topo II.
  • Analyzed both naked DNA and chromatin substrates under varying torsional stress conditions.

Key Points:

  • Eukaryotic topo II exhibits significantly higher processivity on plectonemic DNA than previously reported, relaxing over 6000 DNA turns.
  • Topo II can relax supercoiled DNA before plectoneme formation, albeit with reduced processivity, and its relaxation rate correlates with decreasing torsion.
  • Chromatinization maintains high topo II processivity under high torsional stress and enhances it even under low torsional stress.

Conclusions:

  • Chromatin acts as a potent stimulant for type IIA topoisomerase function.
  • The structural features of chromatin facilitate enhanced topo II activity, even when DNA torsion is low.