Project description:Initiation of eukaryotic DNA replication requires temporal separation of helicase loading from helicase activation and replisome assembly. Using an in vitro assay for eukaryotic origin-dependent replication initiation, we investigated the control of these events. After helicase loading, we found that the Dbf4-dependent Cdc7 kinase (DDK) initially drives origin recruitment of Sld3 and the Cdc45 helicase-activating protein. Corresponding in vivo studies found that DDK was required for Cdc45 binding at early origins during G1. Upon activation of S-phase cyclin-dependent kinases (S-CDK), a second helicase-activating protein (GINS) and the remainder of the replisome are recruited to the origin. Investigation of DNA polymerase recruitment showed that Mcm10 and DNA unwinding both were critical for recruitment of the lagging but not leading strand DNA polymerases. Our studies identify distinct roles for DDK and S-CDK during helicase activation and support a model in which the leading strand DNA polymerase is recruited prior to DNA unwinding and initial RNA primer synthesis. We performed chromatin immunoprecipitation (ChIP) against Cdc45 in CDC7 and cdc7-4 cells arrested in G1 phase to assess the requirement of the Dbf4-dependent kinase on the recruitment of Cdc45 to origin DNA during G1.
Project description:Centromeres play several important roles in ensuring proper chromosome segregation. Not only do they promote kinetochore assembly for microtubule attachment, but they also support robust sister chromatid cohesion at pericentromeres and facilitate replication of centromeric DNA early in S phase. However, it is still elusive how centromeres orchestrate all these functions at the same site. Here we show that the budding yeast Dbf4-dependent kinase (DDK) accumulates at kinetochores in telophase, facilitated by the Ctf19 kinetochore complex. This promptly recruits Sld3-Sld7 replication initiator proteins to pericentromeric replication origins so that they initiate replication early in S phase. Furthermore DDK at kinetochores independently recruits the Scc2-Scc4 cohesin loader to centromeres in G1 phase. This enhances cohesin loading and facilitates robust pericentromeric cohesion in S phase. Thus, we have found the central mechanism by which kinetochores orchestrate early S phase DNA replication and robust sister chromatid cohesion at microtubule attachment sites. Measurement of genome replication time for various S. cerevisiae strains. For each strain two samples were analysed: a replicating sample (from S phase) and a non-replicating sample (from G2 phase).
Project description:Centromeres play several important roles in ensuring proper chromosome segregation. Not only do they promote kinetochore assembly for microtubule attachment, but they also support robust sister chromatid cohesion at pericentromeres and facilitate replication of centromeric DNA early in S phase. However, it is still elusive how centromeres orchestrate all these functions at the same site. Here we show that the budding yeast Dbf4-dependent kinase (DDK) accumulates at kinetochores in telophase, facilitated by the Ctf19 kinetochore complex. This promptly recruits Sld3-Sld7 replication initiator proteins to pericentromeric replication origins so that they initiate replication early in S phase. Furthermore DDK at kinetochores independently recruits the Scc2-Scc4 cohesin loader to centromeres in G1 phase. This enhances cohesin loading and facilitates robust pericentromeric cohesion in S phase. Thus, we have found the central mechanism by which kinetochores orchestrate early S phase DNA replication and robust sister chromatid cohesion at microtubule attachment sites.
Project description:In eukaryotes, CDC7 kinase is crucial for DNA replication initiation and has been involved in fork processing and replication stress response. Human CDC7 requires the binding of either one of two regulatory subunits, DBF4 and DRF1, for its activity. However, it is unclear whether the two regulatory subunits target CDC7 to a specific set of substrates, thus having different biological functions, or if they act redundantly. Using genome editing technology, we generated an isogenic set of cell lines deficient in either one of the two CDC7-activating subunits: these cells are viable but present signs of genomic instability, indicating that both DBF4 and DRF1 can independently support CDC7 for bulk DNA replication. Nonetheless, DBF4-deficient cells show altered replication efficiency, including partial deficiency in MCM helicase phosphorylation and alterations in the replication timing of discrete genomic regions. Notably, we find that CDC7 function at replication forks is entirely dependent on DBF4 and not DRF1. Thus, DBF4 is the primary regulator of CDC7 activity, likely mediating most of its functions in unperturbed DNA replication and during replication fork processing upon replication interference.
Project description:Initiation of eukaryotic chromosome replication follows a spatiotemporal program. Current model suggests that replication origins compete for a limited pool of initiation factors. However, it remains to be answered how these limiting factors are preferentially recruited to early origins. Here, we report that Dbf4 is enriched at early origins through its interaction with forkhead transcription factors Fkh1 and Fkh2. This interaction is mediated by Dbf4 C-terminus and was successfully reconstituted in vitro. An interaction defective mutant dbf4ΔC phenocopies fkh alleles in terms of origin firing. Remarkably, genome-wide replication profiles reveal that the direct fusion of the DNA-binding domain of Fkh1 to Dbf4 restores the Fkh-dependent origin firing, but specifically interferes with the pericentromeric origin activation. Furthermore, Dbf4 directly interacts with Sld3 and promotes the recruitment of downstream limiting factors. These data suggest that Fkh1 targets Dbf4 to a subset of non-centromeric origins to promote early replication, in a manner that is reminiscent to the recruitment of Dbf4 to pericentromeric origins by Ctf19.
Project description:Eukaryotic genomes are replicated in spatiotemporal patterns that are stereotypical for individual genomes and developmental profiles. In the model system S. cerevisiae, two primary mechanisms determine the preferential activation of replication origins during early S phase, thereby largely defining the consequent replication profiles of these cells. Both mechanisms are thought to act through specific recruitment of a rate-limiting initiation factor, Dbf4-dependent kinase (DDK), to a subset of licensed replication origins. Fkh1/2 is responsible for stimulation of most early-firing origins, except for centromere (CEN)-proximal origins that recruit DDK via the kinetochore protein Ctf19, which is required for their early-firing. The C-terminus of Dbf4 has been implicated in its recruitment to origins via both the Fkh1/2 and Ctf19 mechanisms. Here, we show that the Zn-finger motif within the C-terminus is specifically required for Dbf4 recruitment to CENs to stimulate CEN-proximal/Ctf19-dependent origins, whereas stimulation of origins via the Fkh1/2 pathway remains largely intact. These findings re-open the question of exactly how Fkh1/2 and DDK act together to stimulate replication origin initiation.
Project description:Cdc7 kinase is known to initiate DNA replication, but it is unknown where Cdc7 is found within the genome. We modified the Calling Cards method that uses the Ty5 retrotransposon to investigate Cdc7 binding in the genome. The Ty5 retrotransposon is inserted into the genome by DNA transcription factors or replication factors binding within the genome. We find that Cdc7 inserts Ty5 transposons throughout chromosomes and furthermore creates more Ty5 insertions into regions of DNA that are known to replicate early. Cdc7 does not solely integrate Ty5 at origins or replication, but rather throughout the genome.
Project description:We demonstrate that the Cdc7/Dbf4-dependent histone modification, H3 threonine 45 phosphorylation (H3T45p), is specifically enriched at origins of replication, and highly transcribed genes involved in protein synthesis and glycolysis. Furthermore, we show that H3T45p also mediates polymerase recruitment and expression of these genes.
Project description:Initiation of eukaryotic DNA replication requires temporal separation of helicase loading from helicase activation and replisome assembly. Using an in vitro assay for eukaryotic origin-dependent replication initiation, we investigated the control of these events. After helicase loading, we found that the Dbf4-dependent Cdc7 kinase (DDK) initially drives origin recruitment of Sld3 and the Cdc45 helicase-activating protein. Corresponding in vivo studies found that DDK was required for Cdc45 binding at early origins during G1. Upon activation of S-phase cyclin-dependent kinases (S-CDK), a second helicase-activating protein (GINS) and the remainder of the replisome are recruited to the origin. Investigation of DNA polymerase recruitment showed that Mcm10 and DNA unwinding both were critical for recruitment of the lagging but not leading strand DNA polymerases. Our studies identify distinct roles for DDK and S-CDK during helicase activation and support a model in which the leading strand DNA polymerase is recruited prior to DNA unwinding and initial RNA primer synthesis.