Nucleosome Core Particle Disassembly and Assembly Kinetics Studied Using Single-Molecule Fluorescence

Noa Plavner Hazan, Toma E. Tomov, Roman Tsukanov, Miran Liber, Yaron Berger, Rula Masoud, Katalin Toth, Joerg Langowski, Eyal Nir

Research output: Contribution to journalArticlepeer-review

Abstract

The stability of the nucleosome core particle (NCP) is believed to play a major role in regulation of gene expression. To understand the mechanisms that influence NCP stability, we studied stability and dissociation and association kinetics under different histone protein (NCP) and NaCl concentrations using single-pair Förster resonance energy transfer and alternating laser excitation techniques. The method enables distinction between folded, unfolded, and intermediate NCP states and enables measurements at picomolar to nanomolar NCP concentrations where dissociation and association reactions can be directly observed. We reproduced the previously observed nonmonotonic dependence of NCP stability on NaCl concentration, and we suggest that this rather unexpected behavior is a result of interplay between repulsive and attractive forces within positively charged histones and between the histones and the negatively charged DNA. Higher NaCl concentrations decrease the attractive force between the histone proteins and the DNA but also stabilize H2A/H2B histone dimers, and possibly (H3/H4)2 tetramers. An intermediate state in which one DNA arm is unwrapped, previously observed at high NaCl concentrations, is also explained by this salt-induced stabilization. The strong dependence of NCP stability on ion and histone concentrations, and possibly on other charged macromolecules, may play a role in chromosomal morphology.

Original languageAmerican English
Pages (from-to)1676-1685
Number of pages10
JournalBiophysical Journal
Volume109
Issue number8
DOIs
StatePublished - 23 Oct 2015

All Science Journal Classification (ASJC) codes

  • Biophysics

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