The activity of chromatin-bound protease extracted selectively with histone H2B from calf thymus and rat liver

Proteolytic clipping of histone tails: the emerging role of histone proteases in regulation of various biological processes

Chromatin is a dynamic DNA scaffold structure that responds to a variety of external and internal stimuli to regulate the fundamental biological processes. Majority of the cases chromatin dynamicity is exhibited through chemical modifications and physical changes between DNA and histones. These modifications are reversible and complex signaling pathways involving chromatin-modifying enzymes regulate the fluidity of chromatin. Fluidity of chromatin can also be impacted through irreversible change, proteolytic processing of histones which is a poorly understood phenomenon. In recent studies, histone proteolysis has been implicated as a regulatory process involved in the permanent removal of epigenetic marks from histones. Activities responsible for clipping of histone tails and their significance in various biological processes have been observed in several organisms. Here, we have reviewed the properties of some of the known histone proteases, analyzed their significance in biological processes and have provided future directions.

Study of protein carbonyls in subcellular fractions isolated from liver and spleen of old and gamma-irradiated rats

Age- and gamma-irradiation-dependent accumulation of oxidatively modified proteins (measured as carbonyl level) was studied in cytoplasm, mitochondria and nuclei isolated from spleen and liver of 4- and 26-month-old rats. The protein carbonyl levels significantly increased with age in all fractions studied. The carbonyl content was found to be two times higher in the nuclei than in the mitochondria and cytoplasm, which may be related to an extensive modification of lysine and arginine residues in histone molecules. Gamma-Irradiation of rats with 10 Gy caused a rise of protein carbonyls only in their cytoplasm and mitochondria, which was prevented in the animals fed with antioxidants and vitamins for a month before the irradiation. We observed an activation of histone-specific proteases in the nuclei of gamma-irradiated rats. The lack of carbonyl accumulation in the nuclear proteins isolated from tissues of gamma-irradiated animals may be explained by the degradation of oxidized histones by these proteases.

Chromatin proteins of rat preputial-gland: acute changes in response to estrogen

The effects of estradiol-17 beta (E2 beta) at 2 or 15 min in vivo on chromatin proteins of rat preputial-gland were analyzed by a battery of electrophoretic methods. Among histones, E2 beta/control ratios for major bands of H1 decreased substantially between 2 and 15 min. In contrast, ratios of H4 increased (P less than 0.01), whereas, except for losses by 2 min in a H2B-like component and in H3.1, other core histones were unchanged. Among 0.35 M NaCl-soluble proteins, components at 34K-mol. wt and less than 21K -mol wt were increased after 2 min of E2 beta. The bulk of the hormone-responsive low-molecular weight proteins was basic in charge. Electrophoretic correlates of 6 basic lysosomal proteins corresponded to those of low-molecular weight salt-soluble chromatin proteins. Selective proteolysis initiated in vivo by E2 beta depleted some tightly-bound nonhistone proteins.

Comparative studies on chromatin proteins from chicken thrombocytes and erythrocytes

Comparative studies on chromatin composition, nature of non-histone chromatin proteins, histone fractions and the activity of chromatin-bound protease from chicken thrombocytes and erythrocytes were performed. Chemical analysis of chromatin preparations indicated the lack of an essential difference in the protein/DNA ratio. Analysis of non-histone chromatin proteins in SDS-polyacrylamide gel electrophoresis and isoelectric focusing showed a striking similarity of their electrophoretic patterns. Quantitative rather than qualitative differences predominated. During acidic urea-polyacrylamide gel electrophoresis, it was found that histones from thrombocytes contain a fraction migrating with the electrophoretic mobility of histone H5 from erythrocytes. This fraction constitutes 6.7% and 19% of total histone in thrombocytes and erythrocytes, respectively. The electrophoretic patterns of histones, as well as the amount of peptides soluble in 25% trichloroacetic acid released during incubation of chromatin and isolated histones at pH 8, indicated that the activity of chromatin-bound protease was significantly higher in thrombocytes than in erythrocytes.