Telomerase regulation by the Pif1 helicase: a length-dependent effect?

Stinus, Sonia; Paeschke, Katrin; Chang, Michael

doi:10.1007/s00294-017-0768-6

Cited by 15 publications

(22 citation statements)

References 28 publications

(43 reference statements)

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“…In vivo , limiting concentrations of telomerase [fewer than one telomerase complex per telomere ( Mozdy and Cech, 2006 )] may mean that telomerase released by Pif1 action is unlikely to result in additional telomere elongation. While Pif1 preferentially binds long telomeres in vivo ( Phillips et al, 2015 ), experiments analyzing telomere addition in a single cell cycle are consistent with Pif1 action independent of telomere length, suggesting that enrichment at longer telomeres may reflect roles of Pif1 during replication ( Stinus et al, 2018 ).…”

Section: Regulation Of De Novo Telomere Additionmentioning

confidence: 92%

When the Ends Justify the Means: Regulation of Telomere Addition at Double-Strand Breaks in Yeast

Hoerr

Ngo

Friedman

2021

Front. Cell Dev. Biol.

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Telomeres, repetitive sequences located at the ends of most eukaryotic chromosomes, provide a mechanism to replenish terminal sequences lost during DNA replication, limit nucleolytic resection, and protect chromosome ends from engaging in double-strand break (DSB) repair. The ribonucleoprotein telomerase contains an RNA subunit that serves as the template for the synthesis of telomeric DNA. While telomere elongation is typically primed by a 3′ overhang at existing chromosome ends, telomerase can act upon internal non-telomeric sequences. Such de novo telomere addition can be programmed (for example, during chromosome fragmentation in ciliated protozoa) or can occur spontaneously in response to a chromosome break. Telomerase action at a DSB can interfere with conservative mechanisms of DNA repair and results in loss of distal sequences but may prevent additional nucleolytic resection and/or chromosome rearrangement through formation of a functional telomere (termed “chromosome healing”). Here, we review studies of spontaneous and induced DSBs in the yeast Saccharomyces cerevisiae that shed light on mechanisms that negatively regulate de novo telomere addition, in particular how the cell prevents telomerase action at DSBs while facilitating elongation of critically short telomeres. Much of our understanding comes from the use of perfect artificial telomeric tracts to “seed” de novo telomere addition. However, endogenous sequences that are enriched in thymine and guanine nucleotides on one strand (TG-rich) but do not perfectly match the telomere consensus sequence can also stimulate unusually high frequencies of telomere formation following a DSB. These observations suggest that some internal sites may fully or partially escape mechanisms that normally negatively regulate de novo telomere addition.

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Section: Regulation Of De Novo Telomere Additionmentioning

confidence: 92%

When the Ends Justify the Means: Regulation of Telomere Addition at Double-Strand Breaks in Yeast

Hoerr

Ngo

Friedman

2021

Front. Cell Dev. Biol.

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“…Repetitive unwinding activity may be of particular significance for 5′-3′ helicases, such as those of the SF1B Pif1 family (15,16), whose activity may be coupled to DNA replication. Pif1 from Saccharomyces cerevisiae, the best studied of this class of helicases and its founding member, displaces telomerase from telomeric ends (17)(18)(19)(20)(21)(22), facilitates DNA replication at Gquadruplex-forming sequences during lagging strand DNA synthesis (23)(24)(25)(26), cooperates with Dna2 helicase/nuclease in long flap processing during Okazaki fragment maturation (27)(28)(29)(30)(31), and functions with DNA polymerase δ during break-induced DNA replication (32)(33)(34)(35). Similarly, Pfh1, the Pif1 homolog in Schizosaccharomyces pombe, functions in many of the same pathways and has biochemical activities similar to Pif1 (36)(37)(38)(39)(40)(41)(42).…”

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confidence: 99%

Branched unwinding mechanism of the Pif1 family of DNA helicases

Singh

Soranno

Sparks

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Members of the Pif1 family of helicases function in multiple pathways that involve DNA synthesis: DNA replication across G-quadruplexes; break-induced replication; and processing of long flaps during Okazaki fragment maturation. Furthermore, Pif1 increases strand-displacement DNA synthesis by DNA polymerase δ and allows DNA replication across arrays of proteins tightly bound to DNA. This is a surprising feat since DNA rewinding or annealing activities limit the amount of single-stranded DNA product that Pif1 can generate, leading to an apparently poorly processive helicase. In this work, using single-molecule Förster resonance energy transfer approaches, we show that 2 members of the Pif1 family of helicases, Pif1 from Saccharomyces cerevisiae and Pfh1 from Schizosaccharomyces pombe, unwind double-stranded DNA by a branched mechanism with 2 modes of activity. In the dominant mode, only short stretches of DNA can be processively and repetitively opened, with reclosure of the DNA occurring by mechanisms other than strand-switching. In the other less frequent mode, longer stretches of DNA are unwound via a path that is separate from the one leading to repetitive unwinding. Analysis of the kinetic partitioning between the 2 different modes suggests that the branching point in the mechanism is established by conformational selection, controlled by the interaction of the helicase with the 3′ nontranslocating strand. The data suggest that the dominant and repetitive mode of DNA opening of the helicase can be used to allow efficient DNA replication, with DNA synthesis on the nontranslocating strand rectifying the DNA unwinding activity.

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“…The increase in telomere extension frequency of tlc1-tm telomeres is much more dramatic than the increase seen in rif1∆, rif2∆, and pif1-m2 cells (Teixeira et al, 2004;Stinus et al, 2017), even though these mutants have similar or longer telomeres than the tlc1-tm mutant (e.g. see Fig.…”

Section: Tlc1-tm Telomeres Are Rapidly Degraded In the Absence Of Telomerasementioning

confidence: 89%

“…(C) Telomere VI-R sequences obtained from the iSTEX analysis in B were binned into groups of 10 nt in size according to telomere length before telomerase induction. iSTEX data for the extension of wild-type telomeres were taken from previous studies (Strecker et al, 2017;Stinus et al, 2017) and included for comparison. Groups containing less than four telomeres were excluded from this analysis.…”

Section: The Role Of G-quadruplexes At S Cerevisiae Telomeresmentioning

confidence: 99%

Rif2 protects Rap1-depleted telomeres from MRX-mediated degradation inSaccharomyces cerevisiae

Bringas

Stinus

Wanders

et al. 2020

Preprint

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SummaryRap1 is the main protein that binds double-stranded telomeric DNA in Saccharomyces cerevisiae. Rap1 can also bind and promote the formation of G-quadruplexes, which are thought to form at telomeres. Examination of the telomere functions of Rap1 is complicated by the fact that it also acts as a transcriptional regulator of hundreds of genes and is encoded by an essential gene. In this study, we disrupt Rap1 telomere association and G-quadruplex formation by expressing a mutant telomerase RNA subunit (tlc1-tm) that introduces mutant telomeric repeats. Remarkably, tlc1-tm cells grow as well as wild-type cells, although depletion of Rap1 at telomeres causes defects in telomere length regulation and telomere capping. We find that Rap1, Rif2, and the Ku complex work in parallel to prevent telomere degradation, and absence of all three causes lethality. The partially redundant mechanisms may explain the rapid evolution of telomere components in budding yeast species.

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Telomerase regulation by the Pif1 helicase: a length-dependent effect?

Cited by 15 publications

References 28 publications

When the Ends Justify the Means: Regulation of Telomere Addition at Double-Strand Breaks in Yeast

When the Ends Justify the Means: Regulation of Telomere Addition at Double-Strand Breaks in Yeast

Branched unwinding mechanism of the Pif1 family of DNA helicases

Rif2 protects Rap1-depleted telomeres from MRX-mediated degradation inSaccharomyces cerevisiae

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