PCNA connects DNA replication to epigenetic inheritance in yeast

Area of Science:

• Molecular Biology
• Epigenetics
• Yeast Genetics

Background:

• Transcriptional silencing in Saccharomyces cerevisiae is mediated by heterochromatin-like structures at HM mating-type loci and telomeres.
• These epigenetic structures are stably inherited through multiple mitotic divisions.

Purpose of the Study:

• To investigate the role of proliferating cell nuclear antigen (PCNA) in maintaining epigenetic gene silencing.
• To elucidate the mechanisms by which PCNA influences chromatin structure inheritance.

Main Methods:

• Analysis of PCNA mutants (pol30-8, pol30-6, pol30-79) for gene silencing defects at telomeres and the HMR locus.
• Assay of silencing using the ADE2 gene reporter system.
• In vitro binding assays and in vivo chromatin association studies with chromatin assembly factor 1 (CAF-1).

Main Results:

• PCNA mutations impaired gene repression near telomeres and at the HMR locus.
• The pol30-8 mutant showed a loss of stable silencing, resulting in mixed repressed and de-repressed cells.
• Other PCNA mutants exhibited synergistic defects with CAF-1 depletion, reduced binding to CAF-1, and altered CAF-1 chromatin association.

Conclusions:

• PCNA plays a critical role in the inheritance of epigenetic chromatin structures during the S phase.
• PCNA contributes to gene silencing through at least two distinct mechanisms involving CAF-1.