Conformational changes of the chromatin subunit

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 75; no. 2; pp. 660 - 663
• Main Authors: Gordon, V.C, Knobler, C.M, Olins, D.E, Schumaker, V.N
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 01.02.1978; National Acad Sciences
• Subjects: Aggregation; animal science; Biochemistry; Chromatin; DNA; Edetic Acid; Histones; Hydrodynamics; Ions; livestock; Logarithms; Models, Chemical; Molecular Conformation; Molecular weight; Monomers; Nucleic acids; Potassium Chloride; zoology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.75.2.660

Hydrodynamic studies on monomer chromatin subunits (ν1) as a function of ionic strength (0.7 mM to 100 mM KCl) indicate two salt-dependent conformational transitions. An abrupt transition occurs at about 7.5 mM ionic strength. Decreasing the ionic strength from 10 to 5 mM results in a decrease in s20,wof the ν1from 11.1 to 9.9 S. The diffusion coefficient D20,wdecreases from 3.3 to 2.7 × 10-7cm2sec-1. The ν1crosslinked with formaldehyde at 10 mM ionic strength do not undergo a similar salt-dependent change in s20,w. Another transition is observed at about 1 mM ionic strength; s20,wdecreases to 9.4 S and D20,wdecreases to 2.2 × 10-7cm2sec-1. Throughout the entire salt range the molecular weight of the ν1remains reasonably constant, implying that salt-dependent changes in the frictional coefficient are being observed. Various hydrodynamic models are considered as possible interpretations of the observed changes in the frictional coefficient.