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S-Cdk-dependent phosphorylation of Sld2 essential for chromosomal DNA replication in budding yeast


Cyclin-dependent protein kinases (Cdks) in eukaryotic cells work as a key enzyme at various points in the cell cycle1,2. At the onset of S phase, active S-phase Cdks (S-Cdks) are essential for chromosomal DNA replication3. Although several replication proteins are phosphorylated in a Cdk-dependent manner3, the biological effects of phosphorylation of these proteins on the activation of DNA replication have not been elucidated. Here we show that Sld2 (ref. 4) (also known as Drc1; ref. 5), one of the replication proteins of budding yeast (Saccharomyces cerevisiae), is phosphorylated in S phase in an S-Cdk-dependent manner, and mutant Sld2 lacking all the preferred Cdk phosphorylation sites (All-A) is defective in chromosomal DNA replication. Moreover, the complex that contains, at least, Sld2 and Dpb11 (ref. 6) (the Sld2–Dpb11 complex4) is formed predominantly in S phase; the All-A protein is defective in this complex formation. Because this complex is suggested to be essential for chromosomal DNA replication4,5, it seems likely that S-Cdk positively regulates formation of the Sld2–Dpb11 complex and, consequently, chromosomal DNA replication.

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Figure 1: Sld2 is phosphorylated during the cell cycle.
Figure 2: Phosphorylation of Sld2 in S phase is required for cell growth.
Figure 3: Phosphorylation of Sld2 is required for formation of the Sld2–Dpb11 complex.
Figure 4: Increased dosage of DPB11 suppresses the growth defect of SLD2 All-A mutant cells.


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We thank T. Iida, J. F. X. Diffley, K. Labib, H. Wong, S. Elledge, K. Sugimoto and H. Masukata for strains and plasmids; T. Kishi and H. Seino for PSTAIRE antibody and discussions; P. Russell for information regarding the unpublished results; and J. F. X. Diffley, K. Labib, H. Masukata, H. Takisawa and A. Sugino for critical reading of the manuscript. This study is partially supported by grants-in-aid from the Ministry of Education, Culture, Sports, Science and Technology, Japan, to H.A. H.M. was a postdoctoral fellow in the National Institute of Genetics.

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Correspondence to Hiroyuki Araki.

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Masumoto, H., Muramatsu, S., Kamimura, Y. et al. S-Cdk-dependent phosphorylation of Sld2 essential for chromosomal DNA replication in budding yeast. Nature 415, 651–655 (2002).

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