Cdc7p-Dbf4p Regulates Mitotic Exit by Inhibiting Polo Kinase

Abstract

Cdc7p-Dbf4p is a conserved protein kinase required for the initiation of DNA replication. The Dbf4p regulatory subunit binds Cdc7p and is essential for Cdc7p kinase activation, however, the N-terminal third of Dbf4p is dispensable for its essential replication activities. Here, we define a short N-terminal Dbf4p region that targets Cdc7p-Dbf4p kinase to Cdc5p, the single Polo kinase in budding yeast that regulates mitotic progression and cytokinesis. Dbf4p mediates an interaction with the Polo substrate-binding domain to inhibit its essential role during mitosis. Although Dbf4p does not inhibit Polo kinase activity, it nonetheless inhibits Polo-mediated activation of the mitotic exit network (MEN), presumably by altering Polo substrate targeting. In addition, although dbf4 mutants defective for interaction with Polo transit S-phase normally, they aberrantly segregate chromosomes following nuclear misorientation. Therefore, Cdc7p-Dbf4p prevents inappropriate exit from mitosis by inhibiting Polo kinase and functions in the spindle position checkpoint.

Budding Yeast Dbf4 Sequences Required for Cdc7 Kinase Activation and Identification of a Functional Relationship Between the Dbf4 and Rev1 BRCT Domains

“…The dbf4-ND109 mutant retains the BRCT-like sequence (including motif N) and motif M, has essentially wild-type growth characteristics, kinase activity, and S-phase progression and activates replication origins as does the wild type (Gabrielse et al 2006). As far as we have determined, this mutant behaves exactly as does the wild type with the exception that it removes a nonessential region that interacts with Polo kinase to inhibit mitotic exit (Miller et al 2009). Therefore, it is possible that, because of their slowed S-phase (see below), the C-terminal mutants activate fewer replication origins and depend upon G 2 /M checkpoint mechanisms to delay entry into or exit from mitosis.…”

“…The Dbf4 N terminus contains a destruction box, two classic NLSs, and residues that bind Cdc5 (Hardy and Pautz 1996;Miller et al 2009) and Rad53 (Kihara et al 2000;Duncker et al 2002). In addition, Dbf4 contains a BRCT-like domain from residues $117-218.…”

Regulation of the final stage of mitosis by components of the pre-replicative complex and a polo kinase

“…17 Further data indicating a role for pre-RC components in mitosis are reports showing that Dbf4/Cdc7, one of the major kinases involved in pre-RC initiation, interacts with Plk1 and regulates mitotic exit by blocking Plk1 in budding yeast. 19,20 The depletion of Dbf4 leads to nuclear segregation defects and misorientated spindles. 20 The evidence that the deficiency of pre-RC components results in common mitotic defects suggests that pre-RC components are tightly connected with roles in mitotic progression or exit before pre-RCs form.…”

“…19,20 The depletion of Dbf4 leads to nuclear segregation defects and misorientated spindles. 20 The evidence that the deficiency of pre-RC components results in common mitotic defects suggests that pre-RC components are tightly connected with roles in mitotic progression or exit before pre-RCs form. different ways: by inhibiting Cdk1 and/or by inhibiting PP2A Cdc55 .…”

Aurora promotes cell division during recovery from TOR-mediated cell cycle arrest by driving spindle pole body recruitment of Polo

“…Polo kinases have a characteristic docking domain for phosphorylated serine and/or threonine residues, called the 'Polobox' domain (PBD) in their C-termini (Elia et al, 2003). Additional phosphorylation-independent substrate interaction motifs exist alongside the phosphorylation-dependent docking motifs within this PBD (Miller et al, 2009). Outside the PBD, Nterminal catalytic and linker (between the kinase domain and the PBD) regions have also been shown to influence Polo localisation (Garcia-Alvarez et al, 2007;Petersen and Hagan, 2005).…”