Abstract
The replication time of Saccharomyces cerevisiae telomeres responds to TG1–3 repeat length, with telomeres of normal length replicating late during S phase and short telomeres replicating early. Here we show that Tel1 kinase, which is recruited to short telomeres, specifies their early replication, because we find a tel1Δ mutant has short telomeres that nonetheless replicate late. Consistent with a role for Tel1 in driving early telomere replication, initiation at a replication origin close to an induced short telomere was reduced in tel1Δ cells, in an S phase blocked by hydroxyurea. The telomeric chromatin component Rif1 mediates late replication of normal telomeres and is a potential substrate of Tel1 phosphorylation, so we tested whether Tel1 directs early replication of short telomeres by inactivating Rif1. A strain lacking both Rif1 and Tel1 behaves like a rif1Δ mutant by replicating its telomeres early, implying that Tel1 can counteract the delaying effect of Rif1 to control telomere replication time. Proteomic analyses reveals that in yku70Δ cells that have short telomeres, Rif1 is phosphorylated at Tel1 consensus sequences (S/TQ sites), with phosphorylation of Serine-1308 being completely dependent on Tel1. Replication timing analysis of a strain mutated at these phosphorylation sites, however, suggested that Tel1-mediated phosphorylation of Rif1 is not the sole mechanism of replication timing control at telomeres. Overall, our results reveal two new functions of Tel1 at shortened telomeres: phosphorylation of Rif1, and specification of early replication by counteracting the Rif1-mediated delay in initiation at nearby replication origins.
Highlights
Chromosomal DNA replication occurs according to a regulated program, with some replication origins initiating early and others late in S phase [1,2]
The ends of chromosomes are protected by specialized structures called telomeres, which prevent their recognition as DNA breaks and enable recruitment of telomerase, the reverse transcriptase that maintains telomere length by replacing terminal TG-repeat sequences lost during successive rounds of DNA replication
We find that Tel1 phosphorylates Rif1 at short telomeres, our investigation shows this phosphorylation is not the sole mechanism through which Tel1 prevents Rif1-mediated replication delay
Summary
Chromosomal DNA replication occurs according to a regulated program, with some replication origins initiating early and others late in S phase [1,2]. The replication time of S. cerevisiae telomeric regions is regulated by telomere length; chromosome regions close to telomeres with a normal length terminal TG1–3 tract generally replicate late, but those close to telomeres with a shortened TG1–3 tract replicate early [3,4]. This control is mediated through altered initiation time of replication origins. How cells detect and respond to telomere length in order to control the replication time of telomeres remains unclear
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.
