The effect of salt on oligocation-induced chromatin condensation.
Condensation of model chromatin in the form of fully saturated 12-mer nucleosome arrays, induced by addition of cationic ligands (ε-oligolysines with charge varied from +4 to +11), was studied in a range of KCl concentrations (10-500mM) using light scattering and precipitation assay titrations. The dependence of EC(50) (ligand concentration at the midpoint of the array condensation) on C(KCl) displays two regimes, a salt-independent at low C(KCl) and a salt-dependent at higher salt concentrations. In the salt-dependent regime EC(50) rises sharply with increase of C(KCl). Increase of ligand charge shifts the transition from the salt-independent to salt-dependent regime to higher salt. In the nucleosome array system, due to the partial neutralization of the DNA charge by histones, a lower oligocation concentration is needed to provoke condensation in the salt-independent regime compared to the related case of DNA condensation by the same cation. In the physiological range of salt concentrations (C(KCl)=50-300mM), K(+) ions assist array condensation by shifting EC(50) of the ε-oligolysines to lower values. At higher C(KCl), K(+) competes with the cationic ligands, which leads to increase of EC(50). Values of salt-dependent dissociation constant for the ε-oligolysine-nucleosome array interaction were obtained, by fitting to a general equation developed earlier for DNA, describing the dependence of EC(50) on dissociation constant, salt and polyelectrolyte concentrations.
School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551 Singapore, Singapore. Korolev@ntu.edu.sg
Nikolay
N
Korolev
Yongqian
Y
Zhao
Abdollah
A
Allahverdi
Khee Dong
KD
Eom
James P
JP
Tam
Lars
L
Nordenskiöld
D002412:Cations / Q000737:chemistry; D002843:Chromatin / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry; D006657:Histones / Q000737:chemistry; D046228:Microarray Analysis; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000737:chemistry; D011107:Polylysine / Q000737:chemistry*; D011189:Potassium Chloride / Q000737:chemistry*; D012492:Salts / Q000737:chemistry
D002412:Cations; D002843:Chromatin; D004573:Electrolytes; D006657:Histones; D009707:Nucleosomes; D012492:Salts; D011107:Polylysine; D011189:Potassium Chloride; D004247:DNA