Nucleosome Core Particle Disassembly and Assembly Kinetics Studied Using Single-Molecule Fluorescence.
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.
Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Noa Plavner
NP
Hazan
Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Toma E
TE
Tomov
Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Roman
R
Tsukanov
Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Miran
M
Liber
Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Yaron
Y
Berger
Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Rula
R
Masoud
Division of Biophysics of Macromolecules, German Cancer Research Center, Heidelberg, Germany.
Katalin
K
Toth
Division of Biophysics of Macromolecules, German Cancer Research Center, Heidelberg, Germany.
Joerg
J
Langowski
Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, Israel. Electronic address: eyalnir@bgu.ac.il.
Eyal
E
Nir
D000818:Animals; D019281:Dimerization; D004926:Escherichia coli; D005453:Fluorescence; D031541:Fluorescence Resonance Energy Transfer; D007700:Kinetics; D009707:Nucleosomes / Q000378:metabolism*; D012965:Sodium Chloride / Q000737:chemistry; D014982:Xenopus laevis
D009707:Nucleosomes; D012965:Sodium Chloride