CDK-dependent complex formation between replication proteins Dpb11, Sld2, Pol (epsilon}, and GINS in budding yeast

DNA replication in eukaryotes depends on cyclin-dependent kinase (CDK) activity. It was already known that CDK phosphorylates replication proteins Sld3 and Sld2, and that phosphorylation enables their interaction with Dpb11. These interactions are essential for replication initiation. However, the mechanism by which these interactions activate replication remained unclear. No prior work had resolved how CDK activity translates into complex formation or replication initiation. This gap motivated the investigation of CDK-dependent complex assembly. The role of Dpb11 in replication initiation was previously established, but its interaction partners beyond Sld2 and Sld3 were not fully characterized. The function of Pol epsilon in replication was known, but its involvement in CDK-regulated complexes was uncertain. The GINS complex was known to assist replication, but its role in CDK-regulated events was not clear.

The study aimed to determine how CDK activity leads to DNA replication initiation in budding yeast. The specific problem addressed was the lack of understanding about how CDK-regulated interactions between Dpb11 and Sld2 promote replication. The researchers sought to identify the downstream effect of these phosphorylation events. They focused on whether CDK activity promotes the formation of a new replication-related complex. The motivation was to clarify the molecular mechanism of CDK-dependent replication initiation. The study also aimed to test whether this complex is essential for replication. The goal was to provide a mechanistic link between CDK activity and replication initiation. The researchers hypothesized that CDK promotes the assembly of a complex containing replication factors.

The researchers used budding yeast as a model system. They performed genetic and biochemical experiments to analyze protein interactions. They tested whether CDK phosphorylation of Sld2 is required for complex formation. They used in vitro assays to examine interactions between Pol epsilon, GINS, Dpb11, and Sld2. They assessed whether complex formation occurs independently of DNA replication. They evaluated the role of Dbf4-dependent Cdc7 kinase in complex assembly. They analyzed genetic interactions between the proteins of interest. They used yeast strains with mutations in relevant genes to assess complex formation. The experiments combined genetic, biochemical, and in vitro approaches.

The study found that CDK promotes the formation of a fragile complex called the preloading complex (pre-LC). This complex includes Pol epsilon, GINS, Dpb11, and CDK-phosphorylated Sld2. Formation of the pre-LC requires phosphorylation of Sld2 by CDK. The complex forms independently of DNA replication. The complex forms independently of protein association with replication origins. The complex forms independently of Dbf4-dependent Cdc7 kinase. The pre-LC was observed in vitro using purified proteins. Genetic interactions suggest that the pre-LC is essential in cells. These findings indicate that CDK regulates replication initiation through pre-LC formation.

The authors propose that CDK regulates DNA replication initiation in budding yeast through pre-LC formation. The pre-LC contains Pol epsilon, GINS, Dpb11, and CDK-phosphorylated Sld2. The formation of the pre-LC is essential for replication initiation. The complex forms independently of DNA replication or Dbf4-dependent Cdc7 kinase. The pre-LC was observed in vitro and in vivo. The findings suggest that CDK activity is sufficient to promote complex formation. The pre-LC may serve as a platform for replication initiation. The authors suggest that CDK regulates replication through this newly identified complex.