RAP1 and telomere structure regulate telomere position effects in Saccharomyces cerevisiae

Area of Science:

• Molecular Biology
• Yeast Genetics
• Epigenetics

Background:

• Telomere position effects influence gene expression near chromosome ends.
• The Rap1 protein (telomere, silencing, and UAS-binding protein) is a key regulator in yeast.
• The RIF1 gene product interacts with the carboxyl terminus of Rap1.

Purpose of the Study:

• To investigate the role of the yeast Rap1 protein's carboxyl terminus in telomere position effects.
• To characterize the function of RIF1 in relation to Rap1 and telomere regulation.
• To determine the impact of telomeric tract length on telomere position effects.

Main Methods:

• Characterization of rap1 mutant alleles (rap1t) lacking the carboxyl terminus.
• Analysis of rif1 null mutants.
• Assessment of telomere position effects and HML locus silencing.
• In vivo accessibility assays using E. coli dam methylase.
• Correlation of telomere tract length (poly(G1-3T)) with transcriptional repression.

Main Results:

• Loss of Rap1's carboxyl terminus abolished telomere position effects and diminished HML silencing.
• Rap1 carboxyl terminus is required for telomere position effects.
• rif1 deletion mutants showed increased frequency of repressed cells.
• Telomere position effects are sensitive to telomeric tract size.
• Longer poly(G1-3T) tracts increased transcriptional repression at telomeres.

Conclusions:

• The carboxyl-terminal domain of Rap1 is crucial for mediating telomere position effects.
• Telomeric poly(G1-3T) tracts actively contribute to the formation or stability of subtelomeric transcriptional states.
• Rif1 acts antagonistically to Rap1 in regulating gene repression at telomeres.