Chromatin associated protease from calf thymus.

We have identified and purified a chromatin bound protease from calf thymus. The purified enzyme cleaves histone H1 when whole histone is used as substrate. The enzyme is inhibited by Soya bean trypsin inhibitor, but not by PMSF, EDTA, pepstatin or Ellman's reagent. Further studies have shown that H1(0) and histone H5 are also cleaved by this enzyme, and that when HMG 1 and 2 are used as substrate HMG1 alone is degraded to give specific degradation products. We have also shown that the enzyme co-isolates with whole histone prepared by acid extraction of calf thymus nuclei, but interestingly it is not present in whole histone samples prepared in the same manner from pig thymus. A second chromatin bound protease which specifically cleaves histone H3 when whole histone is used as substrate has also been identified during the course of this work.