A Late Mitotic Regulatory Network Controlling Cyclin Destruction inSaccharomyces cerevisiae

Abstract

Exit from mitosis requires the inactivation of mitotic cyclin-dependent kinase–cyclin complexes, primarily by ubiquitin-dependent cyclin proteolysis. Cyclin destruction is regulated by a ubiquitin ligase known as the anaphase-promoting complex (APC). In the budding yeast Saccharomyces cerevisiae, members of a large class of late mitotic mutants, including cdc15,cdc5, cdc14, dbf2, andtem1, arrest in anaphase with a phenotype similar to that of cells expressing nondegradable forms of mitotic cyclins. We addressed the possibility that the products of these genes are components of a regulatory network that governs cyclin proteolysis. We identified a complex array of genetic interactions among these mutants and found that the growth defect in most of the mutants is suppressed by overexpression of SPO12, YAK1, andSIC1 and is exacerbated by overproduction of the mitotic cyclin Clb2. When arrested in late mitosis, the mutants exhibit a defect in cyclin-specific APC activity that is accompanied by high Clb2 levels and low levels of the anaphase inhibitor Pds1. Mutant cells arrested in G1 contain normal APC activity. We conclude that Cdc15, Cdc5, Cdc14, Dbf2, and Tem1 cooperate in the activation of the APC in late mitosis but are not required for maintenance of that activity in G1.

The Plk3-Cdc25 circuit

“…The Schizosaccharomyces pombe plo1 À mutant displays similar phenotypes, such as the formation of monopolar spindles and a failure in septum formation after nuclear division (Ohkura et al, 1995), and the budding yeast Plk homolog, Cdc5, seems to play an important role in actin ring formation and cytokinesis (Song and Lee, 2001). Other studies in yeast show that the APC-dependent destruction of Clb2 (cyclin B) depends on Cdc5 activity Jaspersen et al, 1998;Shirayama et al, 1998). In mammalian cells, Plk1 phosphorylates at least three components of the APC, and in an in vitro-reconstituted system, it activates APC to ubiquitinate cyclin B (Kotani et al, 1998).…”

The Role of the Polo Kinase Cdc5 in Controlling Cdc14 Localization

“…It, thus, comes as a surprise that Spo12 is a potent promoter of Cdc14 release from the nucleolus and exit from mitosis when overexpressed during anaphase. High levels of Spo12 allow temperature-sensitive tem1-3, cdc15-2, cdc5-1, and dbf2-2 mutants to grow with almost wild-type kinetics at the restrictive temperature (Parkes and Johnston, 1992;Jaspersen et al, 1998;Shah et al, 2001). To further complicate the Spo12 puzzle, despite overproduced Spo12 effectively promoting Cdc14 release during anaphase even in the absence of a functional MEN, Spo12 fails to induce Cdc14 release from the nucleolus in stages of the cell cycle when Cdc14 is normally sequestered.…”

GPI7 Involved in Glycosylphosphatidylinositol Biosynthesis Is Essential for Yeast Cell Separation

“…It plays multiple key roles in the coordination of mitosis (30,45). CDC5 was identified as a multicopy suppressor of various mutants related to progression of the M phase, such as CDC15, CDC20, DBF2, and TEM1 (46,47). CDC5 was also obtained as a multicopy suppressor of an allele of DBF4, which arrests at the G 1 phase of the cell cycle (48).…”