Project description:Telomere chromatin structure is pivotal for maintaining genome stability by regulating the binding of telomere-associated proteins and inhibition of a DNA damage response. In yeast, the silent information regulator (Sir) proteins bind to terminal telomeric repeats and to subtelomeric X-elements resulting in histone deacetylation and transcriptional silencing. Herein, we show that sir2 mutant strains display a very specific loss of a nucleosome residing in the X-element. Most yeast telomeres contain an X-element and the nucleosome occupancy defect in sir2 mutants is remarkably consistent between different telomeres.
Project description:Transcriptionally silent heterochromatin preferentially localizes at the nuclear periphery, but, despite this, certain budding yeast genes relocate to the nuclear periphery following gene activation, implicating the nuclear envelope in both transcriptional activation and silencing. It is unclear how these distinct chromatin domains are established, maintained and distinguished from one another at the nuclear envelope. Here we report that nuclear pore complexes (NPCs) facilitate the transition between chromatin states by providing a platform to which chromatin-remodeling and chromatin-modifying complexes bind. In particular, we show that the RSC chromatin-remodeling complex associates with NPCs and that the nucleoporin Nup170p nucleates heterochromatin formation at telomeres through recruitment of Sir4p. Deletion of NUP170 altered subtelomeric chromatin structure, reduced SIR complex binding at telomeres, impaired telomeric silencing and abated telomere tethering. These results support a model in which telomeric heterochromatin formation occurs through telomere-NPC interactions that both promote Sir4p binding at telomeres and permit chromatin-remodeling complexes to mediate the transition between chromatin states. Examination of genome-wide nucleosome positions in WT and nup170∆ cells via next-generation sequencing of mononucleosomal DNA.
