Abstract
The function of the replication clamp loaders in the semi-conservative telomere replication and their relationship to telomerase- and recombination mechanisms of telomere addition remains ambiguous. We have investigated the variant clamp loader Ctf18 RFC (Replication Factor C). To understand the role of Ctf18 at the telomere, we first investigated genetic interactions after loss of Ctf18 and TLC1 (the yeast telomerase RNA). We find that the tlc1▵ ctf18▵ double mutant confers a rapid >1000-fold decrease in viability. The rate of loss was similar to the kinetics of cell death in rad52▵ tlc1▵ cells. However, the Ctf18 pathway is distinct from Rad52, required for the repair of DSBs, as demonstrated by the synthetic lethality of rad52▵ tlc1▵ ctf18▵ triple mutants. These data suggest that each mutant elicits non-redundant defects acting on the same substrate. Second, interactions of the yeast hyper-recombinational mutant, mre11A470T, with ctf18▵ confer a synergistic cold sensitivity. The phenotype of these double mutants ultimately results in telomere loss and the generation of recombinational survivors. We observed a similar synergism between single mutants that led to hypersensitivity to the DNA alkylating agent, methane methyl sulphonate (MMS), the replication fork inhibitor hydroxyurea (HU), and to a failure to separate telomeres of sister chromatids. Hence, ctf18▵ and mre11A470T act in different pathways on telomere substrates for multiple phenotypes. The mre11A470T cells also displayed a DNA damage response (DDR) at 15°C but not at 30°C while ctf18▵ mutants conferred a constitutive DDR activity. Both the 15°C DDR pattern and growth rate were reversible at 30°C and displayed telomerase activity in vivo. We hypothesize that Ctf18 confers protection against stalling and/or breaks at the replication fork in cells that either lack, or are compromised for, telomerase activity. This Ctf18-based function is likely to contribute another level to telomere size homeostasis.
Highlights
Telomeres, the nucleic acid/protein complexes present at the termini of eukaryotic chromosomes, provide a means for both end replication and end protection [1]
We find that the growth of telomerase-negative cells is dependent on the clamp loader variant Ctf18 Replication Factor C (RFC)
We have presented several lines of evidence for the involvement of Ctf18 RFC in telomere replication, replication fork repair, and the initiation of cohesion at the telomere
Summary
The nucleic acid/protein complexes present at the termini of eukaryotic chromosomes, provide a means for both end replication and end protection [1]. Pathways of recombinational lengthening occur less frequently, normally when under selection for genome stability. A multiplicity of specific end binding, recombinational, and repair factors act at the telomere. These processes have been intensively studied, less is known about the integration of semiconservative replication in telomere stability and telomere tract size homeostasis. CTF18 encodes one of three variants of the Replication Factor C (RFC) large subunit Rfc: Ctf, Elg, and Rad24 [3,4]. Each of the variant complexes performs both specialized and redundant roles in PCNA-
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
