Yeast telomerase and the SUN domain protein Mps3 anchor telomeres and repress subtelomeric recombination

Abstract

Telomeres form the ends of linear chromosomes and protect these ends from being recognized as DNA doublestrand breaks. Telomeric sequences are maintained in most cells by telomerase, a reverse transcriptase that adds TG-rich repeats to chromosome ends. In budding yeast, telomeres are organized in clusters at the nuclear periphery by interactions that depend on components of silent chromatin and the telomerase-binding factor yeast Ku (yKu). In this study, we examined whether the subnuclear localization of telomeres affects end maintenance. A telomere anchoring pathway involving the catalytic yeast telomerase subunits Est2, Est1, and Tlc1 is shown to be necessary for the perinuclear anchoring activity of Yku80 during S phase. Additionally, we identify the conserved Sad1-UNC-84 (SUN) domain protein Mps3 as the principal membrane anchor for this pathway. Impaired interference with Mps3 anchoring through overexpression of the Mps3 N terminus in a tel1 deletion background led to a senescence phenotype and to deleterious levels of subtelomeric Y9 recombination. This suggests that telomere binding to the nuclear envelope helps protect telomeric repeats from recombination. Our results provide an example of a specialized structure that requires proper spatiotemporal localization to fulfill its biological role, and identifies a novel pathway of telomere protection.[Keywords: Telomere protection; telomerase; nuclear envelope; Sad1/UNC-84 (SUN) homology domain; Mps3; nuclear organization; ATM homolog Tel1] Supplemental material is available at http://www.genesdev.org.

Perinuclear tethers license telomeric DSBs for a broad kinesin- and NPC-dependent DNA repair process

“…1b). Many proteins including the Ku complex (composed of Ku70 and Ku80) and telomerase contribute to a perinuclear telomere-tethering process that is somewhat distinct from cohibin-dependent tethering 13,20,37,38 . Since Ku disruption is ineffectual in our subtelomeric DSB survival assay (Fig.…”

“…These telomeric clusters do not co-localize with nuclear pore complexes 17 . Intriguingly, the ability to survive a subtelomeric DSB is dependent on Nup84 as well as a number of factors known to anchor telomere clusters to the nuclear envelope 12,13,[18][19][20][21][22] . However, the relationship between perinuclear telomere tethers and nuclear pore subcomplexes in subtelomeric DNA repair remains unknown 12,23 .…”

Opening the DNA repair toolbox: Localization of DNA double strand breaks to the nuclear periphery

“…28 Indeed, a recent study suggests that Mps3 provides the primary anchor that tethers telomeres to the nuclear periphery. 46 Thus these data suggest that eroded telomeres, much like DSBs that fail to form a de novo telomere, may re-localize from Mps3 sites on the nuclear membrane to NPCs.…”

Nuclear organization in genome stability: SUMO connections

“…In contrast, alternative recombination and repair pathways, which act on collapsed replication forks, may be facilitated by processing events at nuclear pores through action of the Slx5/Slx8 complex (green) [53,59]. Peripheral tethering of telomeres by an inner nuclear membrane protein Mps3 contributes to the suppression of recombination [65,68]. In the nucleolus (gold) the rDNA repeats are bound to the inner nuclear membrane by the yeast protein Heh1 [69].…”

“…(5) This degradation is proposed to facilitate appropriate repair (modified with permission from [53]). (C) The SUN domain protein Mps3 tethers telomeres to the nuclear periphery, thereby contributing to the suppression of recombination between telomeric repeats [65,68]. Peripheral tethering possibly limits the access of the telomeric repeats to the recombinational machinery mediating sister chromatid exchange, which was shown to be enriched in the nuclear interior [67].…”