Ionic strength-dependent conformational transitions of chromatin. Circular dichroism and thermal denaturation studies

Journal Article · Mon Jan 01 00:00:00 EST 1979 · Biopolymers; (United States)

DOI:https://doi.org/10.1002/bip.1979.360181115· OSTI ID:5308121

Fulmer, A W; Fasman, G D

High-molecular-weight chicken erythrocyte chromatin was prepared by mild digestion of nuclei with micrococcal nuclease. Samples of chromatin containing both core (H3, H4, and H2A, H2B) and lysine-rich (H1, H5) histone proteins (whole chromatin) or only core histone proteins (core chromatin) were examined by CD and thermal denaturation as a function of ionic strength between 0.75 and 7.0 x 10/sup -3/M Na/sup +/. CD studies as 21/sup 0/C revealed a conformational transition over this range of ionic strengths in core chromatin, which indicated a partial unfolding of segment of the core particle DNA at the lowest ionic strength studied. This transition is prevented by the presence of the lysine-rich histones in whole chromatin. Thermal-denaturation profiles of both whole and core chromatins, recorded by hyperchromicity at 260 nm, reproducibly and systematically varied with the ionic strength of the medium. Both materials displayed three resolvable thermal transitions, which represented the total DNA hyperchromicity on denaturation. The fractions of the total DNA which melted in each of these transitions were extremely sensitive to ionic strength. These effects are considered to result from intra- and/or internucleosomal electrostatic repulsions in chromatin studied at very low ionic strengths. Comparison of the whole and core chromatin melting profiles indicated substantial stabilization of the core-particle DNA by binding sites between the H1/H5 histones and the 140-base-pair core particle.

• Research Organization: Brandeis Univ., Waltham, MA
• OSTI ID: 5308121
• Journal Information: Biopolymers; (United States), Vol. 18
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CHROMATIN
MOLECULAR STRUCTURE
IONIC COMPOSITION
BIOLOGICAL EFFECTS
THERMAL DEGRADATION
CHICKENS
DICHROISM
DNA
ERYTHROCYTES
HISTONES
PROTEIN DENATURATION
ANIMALS
BIOLOGICAL MATERIALS
BIRDS
BLOOD
BLOOD CELLS
BODY FLUIDS
FOWL
MATERIALS
NUCLEIC ACIDS
ORGANIC COMPOUNDS
PROTEINS
VERTEBRATES
550200* - Biochemistry
550400 - Genetics