The Cdc14 phosphatase is functionally associated with the Dbf2 protein kinase in Saccharomyces cerevisiae

The Saccharomyces cerevisiae Cdc14 protein phosphatase and Dbf2 protein kinase have been implicated to act during late M phase, but their functions are not known. We report here that CDC14 is a low-copy suppressor of the dbf2-2 mutation at 37 degrees C. The kinase activity of Dbf2 accumulated at a high level, in vivo, during a cdc14 arrest and was also much higher in cdc14 mutant cells at the permissive temperature of growth, therefore in cycling mutant cells than in cycling wild-type cells. This correlated with the accumulation of the more slowly migrating form of Dbf2, previously shown to correspond to the hyperphosphorylated form of the protein. The finding that the dbf2-2 mutation could be rescued following overproduction of catalytically inactive forms of Cdc14 suggested that the control of Dbf2 activity by Cdc14 might be only indirect and independent of Cdc14 phosphatase activity. However, it was found that Cdc14 could form oligomers within the cell, thus leaving open the possibility that catalytically inactive Cdc14 might associate with wild-type Cdc14 and rescue dbf2-2 in a phosphatase-dependent manner. We confirmed that overexpression of CDC14 could rescue mutations in CDC15, which encodes another kinase also implicated to act in late M phase. Cells of a cdc15-2 dbf2-2 double mutant died at temperatures much lower than did either single mutant, whereas there was only a slight additive phenotype in the cdc14-1 dbf2-2 and cdc14-1 cdc15-2 double mutant cells. Finally, functional association between Cdc14 and Dbf2 (and also Cdc15) was confirmed by the finding that the cdc14, dbf2 and cdc15 mutations could be partially rescued by the addition of 1.2 M sorbitol to the culture medium. Our data are the first to demonstrate a functional link between Cdc14 and Dbf2 based on both biochemical and genetic information.