Protein kinase Cdc15 activates the Dbf2-Mob1 kinase complex.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Exit from mitosis is regulated by the protein phosphatase Cdc14.
• Cdc14 activity is controlled by the mitotic exit network (MEN), a complex of proteins including Lte1, Tem1, Cdc5, Cdc15, Dbf2/Dbf20, and Mob1.
• The precise biochemical interactions within the MEN are not fully understood.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the activation of the protein kinase Dbf2.
• To elucidate the role of MEN components, specifically Cdc15 and Mob1, in Dbf2 activation.
• To determine how Dbf2's kinase activity is regulated for proper mitotic exit.

Main Methods:

• In vivo studies to assess Dbf2 kinase activity dependence on MEN components (Tem1, Cdc15, Mob1).
• In vitro biochemical assays using recombinant proteins to study direct interactions and activation.
• Site-directed mutagenesis of conserved phosphorylation sites (Ser-374 and Thr-544) in Dbf2.

Main Results:

• Dbf2 kinase activity in vivo requires Tem1, Cdc15, and Mob1.
• Recombinant Cdc15 directly activates recombinant Dbf2 in vitro, but only in the presence of Mob1.
• Conserved phosphorylation sites Ser-374 and Thr-544 are essential for Dbf2 function and Cdc15-mediated activation, with Mob1 facilitating phosphorylation at these sites.

Conclusions:

• Cdc15 directly activates Dbf2 kinase activity, promoting mitotic exit.
• Mob1 plays a critical role in this activation process by enabling Cdc15 to phosphorylate key sites on Dbf2.
• This study clarifies a crucial step in the MEN pathway, linking Cdc15 and Mob1 to Dbf2 activation for cell cycle progression.