Buoyant density centrifugation of sea urchin embryo chromatin on sucrose-glucose gradient

Unsheared chromatin isolated from sea urchin embryos was submitted to buoyant density centrifugation in sucrose-glucose gradients. The main peak of blastula chromatin was at a density position of 1.299 plus or minus 0.028 plus or minus 0.009 g ml -minus 1 whereas at gastrula stage a shift to a lower bouoyant density position of (1.276 plus or minus 0.021 plus or minus 0.007 g ml minus 1) was observed. Besides the main peak, a small band with a density of 1.18 g ml minus 1 was noticed. The lighter fraction differed from the heavy one in a higher histone to DNA ratio, a lower proportion of the F-1 histone, and a lower nonhistone to DNA ratio. The most pronounced developmental alterations of proteins were observed at the level of nonhistone protein patterns of the light fractions.