[Effect of a substance isolated from the regenerating spleen on the chromatin structural organization and the leukosogenic activity of transplanted cells].

When leukemic cells in vitro are treated with the substance isolated from the regenerating calf spleen, incorporation of 3H-thymidine into DNA is rapidly inhibited. The completeness of DNA synthesis restoration after washing off cells from the substance depends on the duration of the previous contact with the substance. It is the change in the structural organization of chromatin but not the very fact of inhibition of the ability of the cells to the DNA synthesis that is important for a decrease of transplantability of mice cells treated by the substance. The quicker the stability of the DNA/protein interaction in chromatin weakens due to the effect of the substance, the earlier the leukosogenic potential of the treated cells decreases.