Ulp1 is required for subtelomeric chromatin localization and function

  • Author / Creator
    Roesner, Ulyss Karl
  • In yeast, subtelomeric chromatin is silenced and positioned at the inner nuclear membrane (INM) through the interaction of proteins that comprise the heterotrimeric SIR complex with INM proteins. Telomeres reside primarily at the INM using partially redundant tethering mechanisms mediated by the chromatin associated protein, Sir4. Telomere tethering has also been shown to require the posttranslational modification, SUMO (small ubiquitin-related modifier). SUMOylation of target proteins is transient and temporally regulated, with the addition of SUMO to target proteins requiring SUMO ligases and the removal of SUMO being accomplished by isopeptidases. The role of SUMOylation in telomere tethering was first established in studies showing that mutants lacking the SUMO ligase Siz2 show reduced INM association of telomeres, suggesting SUMOylation promotes telomere tethering to the INM. Since SUMO modifications are dynamic, we examined the role of deSUMOylation and the consequences of the accumulation of SUMO conjugates on telomere tethering to the INM. These studies focused on the deSUMOylase, Ulp1. By using the temperature sensitive, ulp1-333 (ulp1ts) allele and the ulp1K352E coiled-coiled (CC) domain point mutant, increases in the accumulation of SUMO conjugates were observed. The accumulation of SUMO conjugates correlates with reduced telomere tethering to the NE at specific points in the cell cycle, with the ulp1ts mutant showing additional defects in subtelomeric silencing and growth. Failing to remove SUMO conjugates attributed to compromised Ulp1 function also caused a loss in the nuclear peripheral association of SIR complex components, Sir4 and Sir3. Mutants expressing the ulp1ts or the ulp1K352E-V53 alleles favored the interaction between the core scaffold nucleoporin, Nup170, with the INM protein Esc1, which has been implicated in necessitating telomere tethering. In addition to this phenotype, the ulp1ts and the ulp1K352E-V53 mutants reduced the interaction between Nup170 and Sir4. The strength of the interaction between Sir4 and Sir3 is also increased in the ulp1ts mutant, suggesting changes in the organization of the SIR complex. Together, these data show that mutations in Ulp1 disrupt subtelomeric silencing and cause a distinct loss of telomere tethering in a cell cycle specific manner.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
  • Degree
    Master of Science
  • DOI
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