REP3-mediated silencing in Saccharomyces cerevisiae

Area of Science:

• Molecular Biology
• Yeast Genetics
• Epigenetics

Background:

• Sir proteins and Rap1p regulate yeast transcriptional silencing.
• Rap1 and Sir4 proteins exhibit DNA anchoring activity, influencing plasmid stability.
• The 2-micron circle REP3 element is a known segregation factor in yeast.

Purpose of the Study:

• To investigate the link between DNA anchoring and transcriptional regulation.
• To determine if the REP3 element can mediate transcriptional silencing.
• To elucidate the role of REP3-binding factors and cohesin in this silencing mechanism.

Main Methods:

• Integration of the REP3 sequence adjacent to the HML locus in yeast strains.
• Analysis of HML transcriptional repression in various mutant yeast strains (e.g., sir deletion, rep1/rep2 deletion, mcd1/scc1 mutation).
• Assessment of silencing in strains lacking the 2-micron circle or overexpressing Rep proteins.

Main Results:

• REP3 confers transcriptional repression on the HML locus, dependent on Sir proteins.
• Repression is reduced in strains lacking REP3-binding factors (Rep1 and Rep2).
• The yeast cohesin complex (MCD1/SCC1) is associated with REP3 and is required for REP3-mediated silencing.
• Conventional silencing is altered by the absence of the 2-micron circle or altered Rep protein levels, suggesting antagonism.

Conclusions:

• The REP3 segregation element can function as a novel transcriptional silencer in yeast.
• This silencing mechanism involves the Sir proteins, the cohesin complex, and is modulated by Rep1 and Rep2 proteins.
• Rep proteins appear to antagonize conventional silencing pathways, highlighting a complex interplay in epigenetic regulation.