Thermodynamics of condensation of nuclear cnromatin. A differential scanning calorimetry study of the salt-dependent structural transitions

Barbara Cavazza, Gianluigi Brizzolara, Giuseppe Lazzarini, Eligio Patrone, Maresa Piccardo, Paola Barboro, Silvio Parodi, Andrea Pasini, Cecilia Balbi

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

We present a detailed thermodynamic investigation of the conformational transitions of chromatin in calf thymus nuclei. Differential scanning calorimetry was used as the leading method, in combination with infrared spectroscopy, electron microscopy, and techniques for the molecular characterization of chromatin components. The conformational transitions were induced by changes in the counterion concentration. In this way, it was possible to discriminate between the interactions responsible for the folding of the higher order structure and for the coiling of nucleosomal DNA. Our experiments confirm that the denaturation of nuclear chromatin at physiological ionic strength occurs at the level of discrete structural domains, the linker and the core particle, and we were able to rule out that the actual denaturation pattern might be determined by dissociation of the nucleohistone complex and successive migration of free histones toward native regions, as recently suggested. The sequence of the denaturation events is (1) the conformational change of the histone complement at 66°C, (2) the unstacking of the linker DNA at 74°C, and (3) the unstacking of the core particle DNA, that can be observed either at 90 or at 107°C, depending on the degree of condensation of chromatin. Nuclear chromatin unfolds in low-salt buffers, and can be refolded by increasing the ionic strength, in accordance with the well-known behavior of short fragments. The process is athermal, therefore showing that the stability of the higher order structure depends on electrostatic interactions. The transition between the folded conformation and the unfolded one proceeds through an intermediate condensation state, revealed by an endotherm at 101°C. The analysis of the thermodynamic parameters of denaturation of the polynucleosomal chain demonstrates that the wrapping of the DNA around the histone octamer involves a large energy change. The most striking observation concerns the linker segment, which melts a few degrees below the peak temperature of naked DNA. This finding is in line with previous thermal denaturation investigations on isolated chromatin at low ionic strength, and suggests that a progressive destabilization of the linker occurs in the course of the salt-induced coiling of DNA in the nucleosome.

Original languageEnglish
Pages (from-to)9060-9072
Number of pages13
JournalBiochemistry
Volume30
Issue number37
Publication statusPublished - 1991

Fingerprint

Differential Scanning Calorimetry
Denaturation
Thermodynamics
Chromatin
Differential scanning calorimetry
Condensation
Salts
DNA
Ionic strength
Histones
Osmolar Concentration
Thymus
Nucleosomes
Coulomb interactions
Static Electricity
Thymus Gland
Electron microscopy
Conformations
Infrared spectroscopy
Spectrum Analysis

ASJC Scopus subject areas

  • Biochemistry

Cite this

Thermodynamics of condensation of nuclear cnromatin. A differential scanning calorimetry study of the salt-dependent structural transitions. / Cavazza, Barbara; Brizzolara, Gianluigi; Lazzarini, Giuseppe; Patrone, Eligio; Piccardo, Maresa; Barboro, Paola; Parodi, Silvio; Pasini, Andrea; Balbi, Cecilia.

In: Biochemistry, Vol. 30, No. 37, 1991, p. 9060-9072.

Research output: Contribution to journalArticle

Cavazza, B, Brizzolara, G, Lazzarini, G, Patrone, E, Piccardo, M, Barboro, P, Parodi, S, Pasini, A & Balbi, C 1991, 'Thermodynamics of condensation of nuclear cnromatin. A differential scanning calorimetry study of the salt-dependent structural transitions', Biochemistry, vol. 30, no. 37, pp. 9060-9072.
Cavazza, Barbara ; Brizzolara, Gianluigi ; Lazzarini, Giuseppe ; Patrone, Eligio ; Piccardo, Maresa ; Barboro, Paola ; Parodi, Silvio ; Pasini, Andrea ; Balbi, Cecilia. / Thermodynamics of condensation of nuclear cnromatin. A differential scanning calorimetry study of the salt-dependent structural transitions. In: Biochemistry. 1991 ; Vol. 30, No. 37. pp. 9060-9072.
@article{2cd6d112e5694980b9b60204c8a44f6a,
title = "Thermodynamics of condensation of nuclear cnromatin. A differential scanning calorimetry study of the salt-dependent structural transitions",
abstract = "We present a detailed thermodynamic investigation of the conformational transitions of chromatin in calf thymus nuclei. Differential scanning calorimetry was used as the leading method, in combination with infrared spectroscopy, electron microscopy, and techniques for the molecular characterization of chromatin components. The conformational transitions were induced by changes in the counterion concentration. In this way, it was possible to discriminate between the interactions responsible for the folding of the higher order structure and for the coiling of nucleosomal DNA. Our experiments confirm that the denaturation of nuclear chromatin at physiological ionic strength occurs at the level of discrete structural domains, the linker and the core particle, and we were able to rule out that the actual denaturation pattern might be determined by dissociation of the nucleohistone complex and successive migration of free histones toward native regions, as recently suggested. The sequence of the denaturation events is (1) the conformational change of the histone complement at 66°C, (2) the unstacking of the linker DNA at 74°C, and (3) the unstacking of the core particle DNA, that can be observed either at 90 or at 107°C, depending on the degree of condensation of chromatin. Nuclear chromatin unfolds in low-salt buffers, and can be refolded by increasing the ionic strength, in accordance with the well-known behavior of short fragments. The process is athermal, therefore showing that the stability of the higher order structure depends on electrostatic interactions. The transition between the folded conformation and the unfolded one proceeds through an intermediate condensation state, revealed by an endotherm at 101°C. The analysis of the thermodynamic parameters of denaturation of the polynucleosomal chain demonstrates that the wrapping of the DNA around the histone octamer involves a large energy change. The most striking observation concerns the linker segment, which melts a few degrees below the peak temperature of naked DNA. This finding is in line with previous thermal denaturation investigations on isolated chromatin at low ionic strength, and suggests that a progressive destabilization of the linker occurs in the course of the salt-induced coiling of DNA in the nucleosome.",
author = "Barbara Cavazza and Gianluigi Brizzolara and Giuseppe Lazzarini and Eligio Patrone and Maresa Piccardo and Paola Barboro and Silvio Parodi and Andrea Pasini and Cecilia Balbi",
year = "1991",
language = "English",
volume = "30",
pages = "9060--9072",
journal = "Biochemistry",
issn = "0006-2960",
publisher = "American Chemical Society",
number = "37",

}

TY - JOUR

T1 - Thermodynamics of condensation of nuclear cnromatin. A differential scanning calorimetry study of the salt-dependent structural transitions

AU - Cavazza, Barbara

AU - Brizzolara, Gianluigi

AU - Lazzarini, Giuseppe

AU - Patrone, Eligio

AU - Piccardo, Maresa

AU - Barboro, Paola

AU - Parodi, Silvio

AU - Pasini, Andrea

AU - Balbi, Cecilia

PY - 1991

Y1 - 1991

N2 - We present a detailed thermodynamic investigation of the conformational transitions of chromatin in calf thymus nuclei. Differential scanning calorimetry was used as the leading method, in combination with infrared spectroscopy, electron microscopy, and techniques for the molecular characterization of chromatin components. The conformational transitions were induced by changes in the counterion concentration. In this way, it was possible to discriminate between the interactions responsible for the folding of the higher order structure and for the coiling of nucleosomal DNA. Our experiments confirm that the denaturation of nuclear chromatin at physiological ionic strength occurs at the level of discrete structural domains, the linker and the core particle, and we were able to rule out that the actual denaturation pattern might be determined by dissociation of the nucleohistone complex and successive migration of free histones toward native regions, as recently suggested. The sequence of the denaturation events is (1) the conformational change of the histone complement at 66°C, (2) the unstacking of the linker DNA at 74°C, and (3) the unstacking of the core particle DNA, that can be observed either at 90 or at 107°C, depending on the degree of condensation of chromatin. Nuclear chromatin unfolds in low-salt buffers, and can be refolded by increasing the ionic strength, in accordance with the well-known behavior of short fragments. The process is athermal, therefore showing that the stability of the higher order structure depends on electrostatic interactions. The transition between the folded conformation and the unfolded one proceeds through an intermediate condensation state, revealed by an endotherm at 101°C. The analysis of the thermodynamic parameters of denaturation of the polynucleosomal chain demonstrates that the wrapping of the DNA around the histone octamer involves a large energy change. The most striking observation concerns the linker segment, which melts a few degrees below the peak temperature of naked DNA. This finding is in line with previous thermal denaturation investigations on isolated chromatin at low ionic strength, and suggests that a progressive destabilization of the linker occurs in the course of the salt-induced coiling of DNA in the nucleosome.

AB - We present a detailed thermodynamic investigation of the conformational transitions of chromatin in calf thymus nuclei. Differential scanning calorimetry was used as the leading method, in combination with infrared spectroscopy, electron microscopy, and techniques for the molecular characterization of chromatin components. The conformational transitions were induced by changes in the counterion concentration. In this way, it was possible to discriminate between the interactions responsible for the folding of the higher order structure and for the coiling of nucleosomal DNA. Our experiments confirm that the denaturation of nuclear chromatin at physiological ionic strength occurs at the level of discrete structural domains, the linker and the core particle, and we were able to rule out that the actual denaturation pattern might be determined by dissociation of the nucleohistone complex and successive migration of free histones toward native regions, as recently suggested. The sequence of the denaturation events is (1) the conformational change of the histone complement at 66°C, (2) the unstacking of the linker DNA at 74°C, and (3) the unstacking of the core particle DNA, that can be observed either at 90 or at 107°C, depending on the degree of condensation of chromatin. Nuclear chromatin unfolds in low-salt buffers, and can be refolded by increasing the ionic strength, in accordance with the well-known behavior of short fragments. The process is athermal, therefore showing that the stability of the higher order structure depends on electrostatic interactions. The transition between the folded conformation and the unfolded one proceeds through an intermediate condensation state, revealed by an endotherm at 101°C. The analysis of the thermodynamic parameters of denaturation of the polynucleosomal chain demonstrates that the wrapping of the DNA around the histone octamer involves a large energy change. The most striking observation concerns the linker segment, which melts a few degrees below the peak temperature of naked DNA. This finding is in line with previous thermal denaturation investigations on isolated chromatin at low ionic strength, and suggests that a progressive destabilization of the linker occurs in the course of the salt-induced coiling of DNA in the nucleosome.

UR - http://www.scopus.com/inward/record.url?scp=0026010433&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0026010433&partnerID=8YFLogxK

M3 - Article

C2 - 1892819

AN - SCOPUS:0026010433

VL - 30

SP - 9060

EP - 9072

JO - Biochemistry

JF - Biochemistry

SN - 0006-2960

IS - 37

ER -