A chromatin-bound proteolytic activity with unique specificity for histone H2A.

Area of Science:

• Biochemistry
• Molecular Biology
• Chromatin Biology

Background:

• Histones are crucial for DNA packaging in chromatin.
• Proteolytic modifications of histones can alter chromatin structure and function.
• The specific proteases involved in histone modification are not fully characterized.

Purpose of the Study:

• To identify and characterize a protease associated with calf thymus chromatin.
• To determine the substrate specificity and cleavage site of the identified protease.
• To investigate the conditions affecting the proteolytic activity.

Main Methods:

• Purification of calf thymus chromatin.
• Enzymatic digestion of histone H2A with the associated protease.
• Analysis of the resulting fragment (cH2A) using acrylamide gel electrophoresis.
• Amino acid analysis and partial sequencing of cH2A.
• Investigation of protease activity under varying ionic strength conditions.

Main Results:

• A protease was identified that specifically cleaves histone H2A, producing a fragment (cH2A).
• cH2A results from the removal of 15 amino acids from the C-terminus of H2A, with valine114 as the new C-terminal residue.
• Proteolytic activity is dependent on high ionic strength, suggesting conformation-specific cleavage.
• The protease is of nuclear origin and tightly associated with chromatin, requiring 1.2 M NaCl for dissociation.

Conclusions:

• A novel H2A-specific nuclear protease associated with chromatin has been identified.
• The protease exhibits conformation-dependent cleavage specificity, influenced by ionic strength.
• This enzyme plays a role in histone modification within the nucleus.