Endogenous proteolytic activity of chromatin

Chromatin from rat liver and Ehrlich ascites tumor (EAT) was isolated by two different procedures and the chromatin preparations were incubated at 37 degrees C. To follow the proteolysis at 0, 4, 8, and 24 hrs, aliquots were taken and analysed by SDS polyacrylamide gel electrophoresis. Although there were some differences in the proteolytic activity of the different chromatins, in general they were found to sustain a several hours incubation without appreciable degradation to occur. However, when prior to incubation the chromatins were dissociated, a rapid proteolysis took place. This shows that there are specific, chromatin bound proteinases that are inactive while immobilized in the chromatin structure and become activated on dissociation.