Saccharomyces cerevisiae RAP1 binds to telomeric sequences with spatial flexibility.

Area of Science:

• Molecular Biology
• Genetics
• Yeast Biology

Background:

• Telomeric sequences exhibit wide divergence across budding yeast species.
• Despite variations, a conserved core sequence matching RAP1-binding sites is present.
• Specific variant repeats exist in Saccharomyces castellii and Saccharomyces dairensis.

Purpose of the Study:

• To investigate the binding of RAP1 protein to conserved and variant telomeric sequences in yeast.
• To characterize the specific DNA sequences involved in RAP1 binding.
• To explore the implications of RAP1 binding for telomeric chromatin structure.

Main Methods:

• DNA sequence analysis of telomeres from different yeast species.
• Electrophoretic mobility shift assays (EMSAs) to study protein-DNA interactions.
• DNase I footprinting to precisely map RAP1 binding sites on DNA.

Main Results:

• RAP1 protein binds the conserved core telomeric sequence, ignoring diverged regions.
• In S. castellii and S. dairensis, RAP1 binding sites are formed by combining two 8 bp repeats.
• DNase I footprinting identified a 13 bp binding site (CTGGGTGTCTGGG) and revealed lower affinity binding to variant repeats, sometimes resulting in split footprints due to DNA looping.
• The bipartite structure of RAP1 may facilitate telomeric chromatin remodeling.

Conclusions:

• RAP1 protein specifically recognizes and binds conserved telomeric sequences in yeast.
• The binding characteristics of RAP1 to variant repeats suggest a role in dynamic telomeric chromatin structures.
• The findings propose that RAP1's structure is key to remodeling telomeric chromatin, impacting its in vivo assembly and organization.