Changes in chromatin proteins during liver regeneration.

The metabolism of chromatin proteins of rat liver has been examined during the prereplicative period following partial hepatectomy. Within 8 hours after partial hepatectomy, isolated chromatin exhibits a 7% decrease in its histone to DNA mass ratio compared to sham-operated and zero time controls. The time course and amount of this decline correlate well with the previously published pattern of chromatin template activity increase. During the decrease in histone, the relative amounts of the five major species remain constant. However, there are differential losses and resyntheses of certain histone species. Histone I shows the most pronounced turnover, an estimated 12.5 %. During regeneration, the non-histone chromatin protein to DNA mass ratio does not change significantly, nor do the electrophoretic patterns of major non-histone polypeptides. However, during the initial period of chromatin template activity increase (from 2% to 4 hours after the operation), the non-histones as a group exhibit an increase in their rate of labeling greater than that of other subcellular fractions. Moreover, the rates of labeling of many non-histone species become differentially stimulated, suggesting that their rates of loss from chromatin have also selectively increased.