| The three dimensional organization of chromatin domains in the nucleus is an important factor in gene regulation. In eukaryotic nuclei, transcriptionally silent chromatin clusters at the nuclear periphery while transcriptionally poised chromatin resides in the nuclear interior. Recent studies show that nuclear pore proteins (NUPs) mediate the positioning of genomic loci at the nuclear periphery, specifically to nuclear pore complexes (NPCs), during gene activation. It has also been suggested that tethering of insulator elements to NPCs is an important factor in chromatin insulator function. Here, I investigate the role of NUPs at a native yeast insulator and examine how NPCs affect the intranuclear position of the silent chromatin domain, HMR. I show that while NUPs localize to the native tDNA insulator adjacent to HMR, loss of NUPs does not compromise insulation. On the contrary, I find that NUPs contribute to silencing at native HMR and are able to restore silencing to a de-repressed HMR allele when tethered to the locus, likely via recruitment to the nuclear periphery. I also demonstrate that loss of Nup60 results in decreased peripheral localization of HMR. Furthermore, I show that loss of telomeric tethering pathways does not eliminate Nup60 localization to HMR, and that HMR colocalizes with NPCs when telomeres are not at the periphery, suggesting that NUPs may mediate an independent pathway for HMR association with the nuclear periphery, and specifically NPCs. I propose that localization of NUPs to the tDNA insulator at HMR helps maintain the intranuclear position of the silent locus, which in turn contributes to the fidelity of silencing at HMR. |
