Reciprocal Association of the Budding Yeast ATM-Related Proteins Tel1 and Mec1 with Telomeres In Vivo

Takata, Hideki; Kanoh, Yutaka; Gunge, Norio; Shirahige, Katsuhiko; Matsuura, Akira

doi:10.1016/s1097-2765(04)00262-x

Cited by 81 publications

(68 citation statements)

References 34 publications

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“…5). Tel1p localizes to telomeres in yeast (Takata et al 2004), and since ATM is recruited to double-strand breaks by Mre11, a member of the Mre11/ Rad50/Nbs1 complex, this could also occur at telomeres (Lee and Paull 2005). In mammals, ATM associates with the double-strand telomere proteins TRF1 and TRF2 (Kishi et al 2001;Karlseder et al 2004), and it is hypothesized that ATM association with telomeric chromatin blocks induction of a DNA damage response (d'Adda di Fagagna et al 2004).…”

Section: Resultsmentioning

confidence: 99%

ATM and ATR make distinct contributions to chromosome end protection and the maintenance of telomeric DNA in Arabidopsis

Vespa¹,

Couvillion²,

Spangler³

et al. 2005

Genes Dev.

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Here we examine the function of ATM and ATR at telomeres in Arabidopsis. Although plants lacking ATM or ATR display wild-type telomere length homeostasis, chromosome end protection is compromised in atm atr mutants. Moreover, atm tert Arabidopsis experience an abrupt, early onset of genome instability, arguing that ATM is required for protection of short telomeres. ATR, by contrast, is required for maintenance of telomeric DNA as telomere shortening is dramatically accelerated in atr tert mutants relative to tert plants. Thus, ATM and ATR make essential and distinct contributions to chromosome end protection and telomere maintenance in higher eukaryotes. Several factors involved in the repair of double-strand breaks in DNA are physically associated with telomeres and have essential roles in chromosome stability (d'Adda di Fagagna et al. 2004). Among them are the phosphatidyl-inositol-3-kinase-like protein kinases (PIKKs) ATM/ Tel1p and ATR/Mec1p/Rad3p, which coordinate the repair, cell-cycle checkpoint, and apoptotic responses to DNA damage (Kastan and Lim 2000;Shiloh 2003). ATM also protects against telomere fusions and participates in telomere length homeostasis as atm/tel1 mutants display shorter telomeres in both mammals and yeast (Lustig and Petes 1986;Smilenov et al. 1997). A telomeric role for ATR has not been explored in mammals because mutants are inviable (Brown and Baltimore 2000;de Klein et al. 2000). However, in yeast mec1-21 mutants, telomeres are shortened (Ritchie et al. 1999). In addition, recent data show that Mec1p facilitates loading of the single-strand telomere-binding protein Cdc13p (Takata et al. 2005). Yeast lacking both Tel1p and Mec1p fail to recruit telomerase and experience progressive telomere erosion (Naito et al. 1998;Ritchie et al. 1999;Chan et al. 2001).Here we explore the role of ATM and ATR at telomeres in Arabidopsis thaliana, a higher eukaryote that tolerates disruption of both of these genes. We find that while neither ATM nor ATR is individually required for telomere length homeostasis, chromosome end protection is impaired in atm atr mutants. Our data further indicate that ATM is involved in protecting chromosome ends in cells with short telomeres, while ATR is required for maintenance of telomeric DNA. Results and DiscussionTo examine the role of ATM and ATR in telomere length regulation, we performed telomere restriction fragment (TRF) analysis on genomic DNA extracted from atm and atr mutants that carry a homozygous T-DNA disruption in the corresponding genes (see Materials and Methods). In yeast and mammals, the absence of ATM/Tel1p leads to shortening of telomeres until they reach a new stable set point (Lustig and Petes 1986;Smilenov et al. 1997). In contrast, atm or atr Arabidopsis displayed wild-type telomere length, even after multiple generations (Fig. 1A). The same result was obtained with mutants doubly deficient in ATM and ATR (Fig. 1A). As previously noted (Culligan et al. 2004), atm atr mutants exhibited no growth defects but were completely sterile. Hence...

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Section: Resultsmentioning

confidence: 99%

ATM and ATR make distinct contributions to chromosome end protection and the maintenance of telomeric DNA in Arabidopsis

Vespa¹,

Couvillion²,

Spangler³

et al. 2005

Genes Dev.

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“…Furthermore, efficient association of Est1 and Est2 with chromosome ends requires Tel1 and Mre11 (which acts in the same pathway as Tel1 for telomere length regulation; Nugent et al 1998;Ritchie and Petes 2000) but not Mec1 (Takata et al 2005;Goudsouzian et al 2006). Tel1 itself is also telomere bound (Takata et al 2004), with enhanced binding to shorter telomeres (Bianchi and Shore 2007;Hector et al 2007;Sabourin et al 2007;Abdallah et al 2009), although there is considerable controversy over the degree and timing of Tel1 association with chromosome termini during the cell cycle. As expected for a key regulator of the interaction between Cdc13 and a telomerase subunit, a tel1-D strain has short telomeres (Lustig and Petes 1986), although telomere length is not impaired enough to confer the Est phenotype displayed by cdc13-2 and est1-60 strains.…”

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confidence: 99%

Telomerase Recruitment in Saccharomyces cerevisiae Is Not Dependent on Tel1-Mediated Phosphorylation of Cdc13

et al. 2010

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In Saccharomyces cerevisiae, association between the Est1 telomerase subunit and the telomere-binding protein Cdc13 is essential for telomerase to be recruited to its site of action. A current model proposes that Tel1 binding to telomeres marks them for elongation, as the result of phosphorylation of a proposed S/TQ cluster in the telomerase recruitment domain of Cdc13. However, three observations presented here argue against one key aspect of this model. First, the pattern of Cdc13 phosphatase-sensitive isoforms is not altered by loss of Tel1 function or by mutations introduced into two conserved serines (S249 and S255) in the Cdc13 recruitment domain. Second, an interaction between Cdc13 and Est1, as monitored by a two-hybrid assay, is dependent on S255 but Tel1-independent. Finally, a derivative of Cdc13, cdc13-(S/ TQ ) 11 /(S/TA) 11 , in which every potential consensus phosphorylation site for Tel1 has been eliminated, confers nearly wild-type telomere length. These results are inconsistent with a model in which the Cdc13-Est1 interaction is regulated by Tel1-mediated phosphorylation of the Cdc13 telomerase recruitment domain. We propose an alternative model for the role of Tel1 in telomere homeostasis, which is based on the assumption that Tel1 performs the same molecular task at double-strand breaks (DSBs) and chromosome termini.

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“…Cdc13-dependent inhibition of Mec1 association with telomeres could explain why Tel1 plays an important role in telomere maintenance. One group reported that Mec1 associates with endogenous telomeres and stimulates recruitment of telomerase to telomeres (Takata et al, 2004;Takata et al, 2005). However, recent studies demonstrated that telomerase recruitment depends largely on Tel1, suggesting that Tel1 associates with endogenous telomeres (Goudsouzian et al, 2006).…”

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Cdc13 Telomere Capping Decreases Mec1 Association but Does Not Affect Tel1 Association with DNA Ends

Hirano

Sugimoto

2007

MBoC

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Chromosome ends, known as telomeres, have to be distinguished from DNA breaks that activate DNA damage checkpoint. Two large protein kinases, ataxia-teleangiectasia mutated (ATM) and ATM-Rad3-related (ATR), control not only checkpoint activation but also telomere length. In budding yeast, Mec1 and Tel1 correspond to ATR and ATM, respectively. Here, we show that Cdc13-dependent telomere capping attenuates Mec1 association with DNA ends. The telomeric TG repeat sequence inhibits DNA degradation and decreases Mec1 accumulation at the DNA end. The TG-mediated degradation block requires binding of multiple Cdc13 proteins. The Mre11-Rad50-Xrs2 complex and Exo1 contribute to DNA degradation at DNA ends. Although the TG sequence impedes Exo1 association with DNA ends, it allows Mre11 association. Moreover, the TG sequence does not affect Tel1 association with the DNA end. Our results suggest that the Cdc13 telomere cap coordinates Mec1 and Tel1 accumulation rather than simply covering the DNA ends at telomeres. INTRODUCTIONDNA double-strand breaks (DSBs) are induced by exogenous DNA-damaging agents and carcinogens or by endogenous by-products, including reactive oxygen species (Friedberg et al., 2006). The repair of DSBs is crucial for maintaining genome stability. All organisms respond to DSBs by promptly launching the DNA damage response. This response involves the recruitment of DNA repair factors and the activation of signal transduction pathways, often termed DNA damage checkpoint pathways (Zhou and Elledge, 2000). Activation of the checkpoint pathway induces cell cycle arrest and expression of genes required for DNA repair.The checkpoint signals are initiated through two large protein kinases, ataxia-teleangiectasia mutated (ATM) and ATM-Rad3-related (ATR) (Zhou and Elledge, 2000;Abraham, 2001). ATM and ATR are highly conserved among eukaryotes. ATR is closely related to Mec1 in the budding yeast Saccharomyces cerevisiae and Rad3 in the fission yeast Schizosaccharomyces pombe. ATM homologues are termed Tel1 in both budding and fission yeasts. Current evidence indicates that the Mre11-Rad50 -Nbs1 (Xrs2 in budding yeast) complex is the primary sensor that recruits ATR/ Mec1 and ATM/Tel1 to DSBs (Nakada et al., 2003a(Nakada et al., , 2004Falck et al., 2005;You et al., 2005). In budding yeast, there is compelling evidence that the Mre11-Rad50 -Xrs2 (MRX) complex collaborates with exonuclease 1 (Exo1) in the generation of single-stranded DNA (ssDNA) at DSB ends (Krogh and Symington, 2004). ATM/Tel1 interacts with the C terminus of Nbs1/Xrs2 to localize to DNA ends (Nakada et al., 2003a;Falck et al., 2005;You et al., 2005). Meanwhile, the ssDNA that is generated at the DSB is covered with replication protein A (RPA) (Wold, 1997;Krogh and Symington, 2004). RPA-covered DNA recruits ATR/Mec1 to a region near the DSB end (Zou and Elledge, 2003;Nakada et al., 2005). ATM and ATR activate the downstream kinases CHK1 and CHK2 with assistance of checkpoint mediators, including 53BP1, BRCA1, and MDC1 (Zhou and Elledge, 2000;Bakke...

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Reciprocal Association of the Budding Yeast ATM-Related Proteins Tel1 and Mec1 with Telomeres In Vivo

Cited by 81 publications

References 34 publications

ATM and ATR make distinct contributions to chromosome end protection and the maintenance of telomeric DNA in Arabidopsis

ATM and ATR make distinct contributions to chromosome end protection and the maintenance of telomeric DNA in Arabidopsis

Telomerase Recruitment in Saccharomyces cerevisiae Is Not Dependent on Tel1-Mediated Phosphorylation of Cdc13

Cdc13 Telomere Capping Decreases Mec1 Association but Does Not Affect Tel1 Association with DNA Ends

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