Intracellular nucleosomes constrain a DNA linking number difference of -1.26 that reconciles the Lk paradox

Nat Commun. 2018 Sep 28;9(1):3989. doi: 10.1038/s41467-018-06547-w.

Abstract

The interplay between chromatin structure and DNA topology is a fundamental, yet elusive, regulator of genome activities. A paradigmatic case is the "linking number paradox" of nucleosomal DNA, which refers to the incongruence between the near two left-handed superhelical turns of DNA around the histone octamer and the DNA linking number difference (∆Lk) stabilized by individual nucleosomes, which has been experimentally estimated to be about -1.0. Here, we analyze the DNA topology of a library of mononucleosomes inserted into small circular minichromosomes to determine the average ∆Lk restrained by individual nucleosomes in vivo. Our results indicate that most nucleosomes stabilize about -1.26 units of ∆Lk. This value balances the twist (∆Tw ≈ + 0.2) and writhe (∆Wr ≈ -1.5) deformations of nucleosomal DNA in terms of the equation ∆Lk = ∆Tw + ∆Wr. Our finding reconciles the existing discrepancy between theoretical and observed measurement of the ΔLk constrained by nucleosomes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Chromosomes, Fungal / genetics
  • DNA Topoisomerases, Type I / metabolism*
  • DNA, Circular / genetics
  • DNA, Circular / metabolism
  • DNA, Fungal / genetics
  • DNA, Fungal / metabolism*
  • Nucleosomes / genetics
  • Nucleosomes / metabolism*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / metabolism*

Substances

  • DNA, Circular
  • DNA, Fungal
  • Nucleosomes
  • Saccharomyces cerevisiae Proteins
  • DNA Topoisomerases, Type I