CHROMATIN CONDENSATION - POSSIBLE DEHYDRATING AND STABILIZING FACTORS

The effect of Na+, Mg2+, spermidine and spermine on the dehydration of chromatin gel and precipitation of soluble chromatin has been compared. Considerable differences have been found in the relative ratios within the studied group (Na+, Mg2+, spermidine and spermine) between the ability to dehydrate (1 : 32 : 53 : 67) and to precipitate (1 : 53 : 800 : 2000) chromatin. On the basis of the dependence of precipitation on initial chromatin concentration it has been suggested that the observed effect as contributed considerably by interparticle aggregation is a relatively good measure of the ability of cation to stabilize higher order structures of chromatin through direct crosslinking or induction of hydrophobic associations at selected sites. In contrary to that the method estimating the direct dehydration measures the overall dehydrating effect of a cation exerted on the whole chromatin. It has been suggested on the basis of the above comparative data that the in vivo regulation of the degree of overall chromatin hydration should occur through changes in concentration of free small inorganic cations. Larger organic polycations like polyamines should be mainly involved in stabilization of the higher order chromatin structures. The stabilizing role of large polyanions like RNA has been ruled out. It has also been found that the unwinding of chromatin DNA results in considerable chromatin hydration. © 1979.