Conformational changes of the chromatin subunit.

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Abstract
Hydrodynamic studies on [chicken erythrocyte] monomer chromatin subunits (v1) as a function of ionic strength (0.7-100 mM KCl) indicate 2 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,w of the v1 from 11.1 to 9.9 S. The diffusion coefficient D20,w decreases from 3.3 to 2.7 .times. 10-7 cm2 s-1. The v1 crosslinked 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,w decreases to 9.4 S and D20,w decreases to 2.2 .times. 10-7 cm2 s-1. Throughout the entire salt range the MW of the v1 remains reasonably constant, implying that salt-dependent chnges in the frictional coefficient are being observed. Various hydrodynamic models are considered as possible interpretations of the observed changes in the frictional coefficient.