The role of the Saccharomyces cerevisiae Cdc7–Dbf4 complex in the replication checkpoint

Abstract

The Cdc7–Dbf4 complex is a conserved serine/threonine protein kinase essential for the initiation of eukaryotic DNA replication. Although an mcm5–bob1 mutation bypasses lethality conferred by mutations in CDC7 or DBF4, the Δcdc7 mcm5–bob1 mutant is sensitive to hydroxyurea (HU), which induces replication stress. To elucidate the reasons for HU sensitivity conferred by deletion of CDC7, we examined the role of Cdc7–Dbf4 in the replication checkpoint. We found that in Cdc7–Dbf4-deficient cells exposed to replication stress, Rad53 remains in a hypophosphorylated form, anaphase spindle is elongated, and checkpoint-specific transcription is not induced. The hypophosphorylated Rad53 exhibits a low autophosphorylation activity, and recombinant Cdc7–Dbf4 phosphorylates Rad53 in vitro. These results suggest that Cdc7–Dbf4 is required for full activation of Rad53 in response to replication stress.