Faculty Opinions recommendation of Break-induced replication and telomerase-independent telomere maintenance require Pol32.

ABSTRACT Broken chromosomes can be repaired by several homologous recombination mechanisms, including gene conversion and break-induced replication (BIR). In Saccharomyces cerevisiae, an HO endonuclease-induced double-strand break (DSB) is normally repaired by gene conversion. Previously, we have shown that in the absence ofRAD52, repair is nearly absent and diploid cells lose the broken chromosome; however, in cells lacking RAD51, gene conversion is absent but cells can repair the DSB by BIR. We now report that gene conversion is also abolished when RAD54, RAD55, and RAD57 are deleted but BIR occurs, as withrad51Δ cells. DSB-induced gene conversion is not significantly affected when RAD50, RAD59, TID1(RDH54), SRS2, or SGS1 is deleted. Various double mutations largely eliminate both gene conversion and BIR, including rad51Δ rad50Δ, rad51Δ rad59Δ, andrad54Δ tid1Δ. These results demonstrate that there is aRAD51- and RAD54-independent BIR pathway that requires RAD59, TID1, RAD50, and presumablyMRE11 and XRS2. The similar genetic requirements for BIR and telomere maintenance in the absence of telomerase also suggest that these two processes proceed by similar mechanisms.

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Control of Translocations between Highly Diverged Genes by Sgs1, the Saccharomyces cerevisiae Homolog of the Bloom'sSyndrome Protein

Molecular and Cellular Biology ◽

10.1128/mcb.00161-06 ◽

2006 ◽

Vol 26 (14) ◽

pp. 5406-5420 ◽

Cited By ~ 52

Author(s):

Kristina H. Schmidt ◽

Joann Wu ◽

Richard D. Kolodner

Keyword(s):

Saccharomyces Cerevisiae ◽

Dna Sequences ◽

Genome Stability ◽

Dna Helicase ◽

Telomere Maintenance ◽

Template Switching ◽

Checkpoint Kinase ◽

Genes Encoding ◽

Atm Protein ◽

Break Induced Replication

ABSTRACT Sgs1 is a RecQ family DNA helicase required for genome stability in Saccharomyces cerevisiae whose human homologs BLM, WRN, and RECQL4 are mutated in Bloom's, Werner, and Rothmund Thomson syndromes, respectively. Sgs1 and mismatch repair (MMR) are inhibitors of recombination between similar but divergent (homeologous) DNA sequences. Here we show that SGS1, but not MMR, is critical for suppressing spontaneous, recurring translocations between diverged genes in cells with mutations in the genes encoding the checkpoint proteins Mec3, Rad24, Rad9, or Rfc5, the chromatin assembly factors Cac1 or Asf1, and the DNA helicase Rrm3. The S-phase checkpoint kinase and telomere maintenance factor Tel1, a homolog of the human ataxia telangiectasia (ATM) protein, prevents these translocations, whereas the checkpoint kinase Mec1, a homolog of the human ATM-related protein, and the Rad53 checkpoint kinase are not required. The translocation structures observed suggest involvement of a dicentric intermediate and break-induced replication with multiple cycles of DNA template switching.

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Oncogenic herpesvirus KSHV triggers hallmarks of alternative lengthening of telomeres

Nature Communications ◽

10.1038/s41467-020-20819-4 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Timothy P. Lippert ◽

Paulina Marzec ◽

Aurora I. Idilli ◽

Grzegorz Sarek ◽

Aleksandra Vancevska ◽

...

Keyword(s):

Cancer Cells ◽

Cell Lines ◽

Telomere Maintenance ◽

Alternative Lengthening Of Telomeres ◽

Telomere Shortening ◽

Alternative Lengthening ◽

A Cell ◽

Infected Cells ◽

Break Induced Replication ◽

Alt Activity

AbstractTo achieve replicative immortality, cancer cells must activate telomere maintenance mechanisms to prevent telomere shortening. ~85% of cancers circumvent telomeric attrition by re-expressing telomerase, while the remaining ~15% of cancers induce alternative lengthening of telomeres (ALT), which relies on break-induced replication (BIR) and telomere recombination. Although ALT tumours were first reported over 20 years ago, the mechanism of ALT induction remains unclear and no study to date has described a cell-based model that permits the induction of ALT. Here, we demonstrate that infection with Kaposi’s sarcoma herpesvirus (KSHV) induces sustained acquisition of ALT-like features in previously non-ALT cell lines. KSHV-infected cells acquire hallmarks of ALT activity that are also observed in KSHV-associated tumour biopsies. Down-regulating BIR impairs KSHV latency, suggesting that KSHV co-opts ALT for viral functionality. This study uncovers KSHV infection as a means to study telomere maintenance by ALT and reveals features of ALT in KSHV-associated tumours.

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Alternative Lengthening of Telomeres Mediated by Mitotic DNA Synthesis Engages Break-Induced Replication Processes

Molecular and Cellular Biology ◽

10.1128/mcb.00226-17 ◽

2017 ◽

Vol 37 (20) ◽

Cited By ~ 72

Author(s):

Jaewon Min ◽

Woodring E. Wright ◽

Jerry W. Shay

Keyword(s):

Dna Synthesis ◽

Telomere Maintenance ◽

Synthesis Process ◽

Loop Formation ◽

Alternative Lengthening Of Telomeres ◽

Independent Manner ◽

Content Type ◽

Alternative Lengthening ◽

Telomere Replication ◽

Break Induced Replication

ABSTRACT Alternative lengthening of telomeres (ALT) is a telomerase-independent telomere maintenance mechanism that occurs in a subset of cancers. By analyzing telomerase-positive cells and their human TERC knockout-derived ALT human cell lines, we show that ALT cells harbor more fragile telomeres representing telomere replication problems. ALT-associated replication defects trigger mitotic DNA synthesis (MiDAS) at telomeres in a RAD52-dependent, but RAD51-independent, manner. Telomeric MiDAS is a conservative DNA synthesis process, potentially mediated by break-induced replication, similar to type II ALT survivors in Saccharomyces cerevisiae. Replication stresses induced by ectopic oncogenic expression of cyclin E, G-quadruplexes, or R-loop formation facilitate the ALT pathway and lead to telomere clustering, a hallmark of ALT cancers. The TIMELESS/TIPIN complex suppresses telomere clustering and telomeric MiDAS, whereas the SMC5/6 complex promotes them. In summary, ALT cells exhibit more telomere replication defects that result in persistent DNA damage responses at telomeres, leading to the engagement of telomeric MiDAS (spontaneous mitotic telomere synthesis) that is triggered by DNA replication stress, a potential driver of genomic duplications in cancer.

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