Telomere looping permits repression "at a distance" in yeast

Area of Science:

• Molecular Biology
• Genetics
• Yeast Biology

Background:

• Transcriptional activators and repressors in yeast typically require proximity to the gene (within 500 base pairs) and usually function upstream.
• A previously proposed mechanism suggests yeast telomeres relieve distance constraints for activators via DNA looping.
• The role of telomeres in enabling distant action of repressors in yeast remained unexplored.

Purpose of the Study:

• To investigate whether the yeast telomere can enable a transcriptional repressor (Tup1) to function at a distance.
• To determine if telomere-mediated repression by Tup1 depends on the Sir3 protein.

Main Methods:

• Constructing yeast strains with the Tup1 binding site tethered 1.5 kb downstream of a reporter gene near a telomere.
• Assessing transcriptional activity using reporter gene assays.
• Evaluating the effect of Sir3 deletion on telomere-mediated Tup1 repression.

Main Results:

• DNA-tethered Tup1 successfully repressed gene transcription when located downstream and 1.5 kb away from the gene, specifically near a yeast telomere.
• This telomere-facilitated repression occurred for both activated and basal transcription levels.
• The observed repression by tethered Tup1 was abolished upon deletion of the Sir3 gene.

Conclusions:

• Yeast telomeres can facilitate the distant action of transcriptional repressors, similar to previously observed effects with activators.
• DNA-tethered Tup1 likely represses transcription by interacting with promoter-bound machinery, with telomere looping enhancing this interaction.
• The Sir3 protein is crucial for telomere-mediated repression by Tup1, suggesting a role in facilitating the interaction loop.