Sir2p exists in two nucleosome-binding complexes with distinct deacetylase activities

Area of Science:

• Molecular Biology
• Epigenetics
• Biochemistry

Background:

• Sir2p is essential for gene silencing via its histone deacetylase activity.
• Conserved Sir2p-like proteins across eukaryotes highlight its fundamental role in gene regulation.
• Understanding Sir2p's function requires characterizing its associated protein complexes.

Purpose of the Study:

• To purify and characterize protein complexes containing Sir2p.
• To investigate the enzymatic activities of these complexes.
• To determine how these complexes interact with nucleosomes.

Main Methods:

• Protein purification techniques to isolate Sir2p-containing complexes.
• Biochemical assays to measure histone deacetylase activity.
• Nucleosome binding assays and enzymatic accessibility studies.

Main Results:

• Two distinct Sir2p-containing complexes were purified: one with Sir4p and another with Net1p.
• The Sir4p-Sir2p complex demonstrated significant NAD-dependent histone deacetylase activity.
• The Net1p-Sir2p complex showed deacetylase activity with minimal NAD-dependence.
• Both complexes efficiently bind to nucleosomes, partially restricting DNA accessibility.

Conclusions:

• Sir2p functions within distinct protein complexes to regulate gene expression.
• The Sir4p-containing complex is a key NAD-dependent histone deacetylase involved in silencing.
• Sir2p complexes play a role in modulating chromatin structure and DNA accessibility.