RESUMEN
Newly copied sister chromatids are tethered together by the cohesin complex, but how sister chromatid cohesion coordinates with DNA replication is poorly understood. Prevailing models suggest that cohesin complexes, bound to DNA before replication, remain behind the advancing replication fork to keep sister chromatids together. By visualizing single replication forks colliding with preloaded cohesin complexes, we find that the replisome instead pushes cohesin to where a converging replisome is met. Whereas the converging replisomes are removed during DNA replication termination, cohesin remains on nascent DNA and provides cohesion. Additionally, we show that CMG (CDC45-MCM2-7-GINS) helicase disassembly during replication termination is vital for proper cohesion in budding yeast. Together, our results support a model wherein sister chromatid cohesion is established during DNA replication termination.
Asunto(s)
Cromátides , Cohesinas , Replicación del ADN , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae , Intercambio de Cromátides Hermanas , Cromátides/metabolismo , Proteínas Cromosómicas no Histona/metabolismo , Cohesinas/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Proteínas de Mantenimiento de Minicromosoma/metabolismo , Proteínas de Unión al ADN/metabolismo , Proteínas Nucleares/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismoRESUMEN
CDC45-MCM2-7-GINS (CMG) helicase assembly is the central event in eukaryotic replication initiation. In yeast, a multi-subunit "pre-loading complex" (pre-LC) accompanies GINS to chromatin-bound MCM2-7, leading to CMG formation. Here, we report that DONSON, a metazoan protein mutated in microcephalic primordial dwarfism, is required for CMG assembly in vertebrates. Using AlphaFold to screen for protein-protein interactions followed by experimental validation, we show that DONSON scaffolds a vertebrate pre-LC containing GINS, TOPBP1, and DNA pol ε. Our evidence suggests that DONSON docks the pre-LC onto MCM2-7, delivering GINS to its binding site in CMG. A patient-derived DONSON mutation compromises CMG assembly and recapitulates microcephalic dwarfism in mice. These results unify our understanding of eukaryotic replication initiation, implicate defective CMG assembly in microcephalic dwarfism, and illustrate how in silico protein-protein interaction screening accelerates mechanistic discovery.