Proper initiation of chromosomal DNA replication requires the Sld3-Sld7 complex in budding yeast

Eukaryotic chromosomal DNA replication initiates from replication origins only once per cell cycle. Many proteins assemble on origins, form replication machinery, and then dissociate from origins to start DNA synthesis. However, the mechanism governing these processes has not been well elucidated. Here, l show that the Sld7 protein participates in the dissociation process between replication machinery and origins. SLD7 (Synthetic Lethality with Dpb 11-24 7), a newly identified gene in a synthetic lethal screening, is not essential for cell growth but required for several cellular processes, such as an efficient chromosomal DNA replication. The Sld7 protein always forms a complex with the Sld3 protein, which functions for the initiation of chromosomal DNA replication, to enhance the Sld3 function. Thus, high-copy SLD3 gene compensates for the lack of Sld7, and high-copy SLD7 gene suppresses the sld3-6 mutation that reduces the complex formation between Sld3 and Sld7 proteins. This Sld3-Sld7 complex associates with replication origins in Gl -phase and dissociates gradualty from them when replication initiates. Sld3 protein associates with and then dissociates from origins in the absence of SId7. The Mcm7 protein, a component of replication machinery, associates with origins and then with neighboring regions of origins as it moves with replication forks. In the absence of Sld7 protein, although Mcm7 associates with origins as efficient as in WT cells, its association with neighboring region is significantly reduced. Therefore, the Sld7 protein seems to help the efficient displacement of replication machinery from origins.