Effect of protease inhibitors on matrix proteins and the association of replicating DNA

Isolation of rat liver nuclear matrices in the presence of the protease inhibitors phenylmethylsulfonyl fluoride (1 mM) or sodium tetrathionate (0.1 mM) results in a 2-4-fold increase in the total amount of matrix proteins, and a 50% increase in the relative proportion of high molecular weight (>100 000 D) matrix polypeptides. Approximately one-third of the total nuclear protein is associated with this less degraded nuclear matrix. Concomitant with the increased preservation of matrix proteins is a 2-5-fold increase in the association of 1 min pulse-labeled, newly replicating DNA.