title: Protein kinase Cdc15 activates the Dbf2-Mob1 kinase complex.
abstract: Exit from mitosis in budding yeast requires inactivation of cyclin-dependent kinases through mechanisms triggered by the protein phosphatase Cdc14. Cdc14 activity, in turn, is regulated by a group of proteins, the mitotic exit network (MEN), which includes Lte1, Tem1, Cdc5, Cdc15, Dbf2/Dbf20, and Mob1. The direct biochemical interactions between the components of the MEN remain largely unresolved. Here, we investigate the mechanisms that underlie activation of the protein kinase Dbf2. Dbf2 kinase activity depended on Tem1, Cdc15, and Mob1 in vivo. In vitro, recombinant protein kinase Cdc15 activated recombinant Dbf2, but only when Dbf2 was bound to Mob1. Conserved phosphorylation sites Ser-374 and Thr-544 (present in the human, Caenorhabditis elegans, and Drosophila melanogaster relatives of Dbf2) were required for DBF2 function in vivo, and activation of Dbf2-Mob1 by Cdc15 in vitro. Although Cdc15 phosphorylated Dbf2, Dbf2-Mob1, and Dbf2(S374A/T544A)-Mob1, the pattern of phosphate incorporation into Dbf2 was substantially altered by either the S374A T544A mutations or omission of Mob1. Thus, Cdc15 promotes the exit from mitosis by directly switching on the kinase activity of Dbf2. We propose that Mob1 promotes this activation process by enabling Cdc15 to phosphorylate the critical Ser-374 and Thr-544 phosphoacceptor sites of Dbf2.
authors.affiliation: Division of Biology and Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Mah
authors.forename: J
authors.initials: J
authors.lastname: Jang
authors.forename: R J
authors.initials: RJ
authors.lastname: Deshaies
mesh_terms: D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D003001:Cloning, Molecular; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D008938:Mitosis; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: C082279:CDC15 protein; D018797:Cell Cycle Proteins; D005656:Fungal Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; C089965:TEM1 protein, S cerevisiae; D011494:Protein Kinases; C085768:DBF2 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D019204:GTP-Binding Proteins; D020559:Monomeric GTP-Binding Proteins