Chromatin-bound protease: (3H)diisopropyl fluorophosphate labeling patterns of chromatin

The nuclei and chromatin of rat liver contain three major proteins reacting with diisopropyl fluorophosphate (DFP). The molecular weights of the three proteins determined by gel filtration in the presence of sodium dodecyl sulfate and sodium dodecyl sulfate-polyacrylamide gel electrophoresis are 70000, 60000, and 25000. The chromatin isolated from whole liver, instead of nuclei, contains an additional DFP-binding protein whose molecular weight is 100000 in the presence of sodium dodecyl sulfate and beta-mercaptoethanol. The small molecular weight DFP-binding protein can be fractionated from chromatin by 0.25 N HC1 and was found to be a protease which is active in the most commonly used solution for chromatin dissociation, that is, 2-3 M NaCl-5 M urea. This enzyme appears to be the major DFP-binding chromatin-bound protease in the chromatin of most rat tissues. The acid-soluble protease is converted from a 25000-dalton form to a 20000-dalton form during 0.25 N HC1 acid extraction from chromatin, which retains proteolytic activity.