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Related Experiment Videos

Linear DNA does not form chromatin containing regularly spaced nucleosomes.

J E Mertz1

  • 1McArdle Laboratory for Cancer Research, University of Wisconsin, Madison, Wisconsin 53706, USA.

Molecular and Cellular Biology
|December 1, 1982
PubMed
Summary

Circular DNA forms regular nucleosomes, unlike linear DNA, suggesting DNA topology influences chromatin structure and gene expression. Proper DNA-histone association is crucial for chromosomal DNA protection and transcription.

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Area of Science:

  • Molecular Biology
  • Epigenetics
  • Genetics

Background:

  • The topological state of DNA is hypothesized to regulate chromatin structure and gene expression in eukaryotes.
  • Understanding DNA's role in chromatin organization is key to deciphering gene regulation mechanisms.

Purpose of the Study:

  • To investigate the impact of DNA topology (circular vs. linear) on nucleosome assembly and chromatin formation.
  • To determine if DNA's structural state affects its susceptibility to degradation and its transcriptional activity.

Main Methods:

  • Incubation of circular and linear simian virus 40 (SV40) DNA in Xenopus oocyte nuclei.
  • Analysis of DNA electrophoretic properties to assess nucleosome arrangement.
  • Micrococcal nuclease digestion to examine DNA fragmentation patterns.

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  • In vitro transcription assays using HeLa cell extracts.

    • Main Results:

    • Circular DNA readily formed regularly spaced nucleosomes (approx. 195 bp intervals), while linear DNA failed to assemble into proper chromatin.
    • Linear DNA that did not form chromatin was degraded, suggesting histones protect DNA from endonucleolytic attack.
    • Linearization of mRNA-encoding DNAs, including SV40, significantly reduced transcriptional activity in Xenopus oocytes.

    Conclusions:

    • DNA topology is critical for proper nucleosome assembly and chromatin formation.
    • Histone association with DNA is essential for protecting chromosomal DNA from degradation.
    • Correct association of DNA with cellular chromosomal factors is a prerequisite for efficient RNA polymerase II transcription.