Type 1 Protein Phosphatase Acts in Opposition to Ipll Protein Kinase in Regulating Yeast Chromosome Segregation

Abstract

The IPL1 gene is required for high-fidelity chromosome segregation in the budding yeast Saccharomyces cerevisiae. Conditional ipl1^ts mutants missegregate chromosomes severely at 37°C. Here, we report that IPL1 encodes an essential putative protein kinase whose function is required during the later part of each cell cycle. At 26°C, the permissive growth temperature, ipl1 mutant cells are defective in the recovery from a transient G2/M-phase arrest caused by the antimicrotubule drug nocodazole. In an effort to identify additional gene products that participate with the Ipll protein kinase in regulating chromosome segregation in yeast, a truncated version of the previously identified DIS2SHGLC7 gene was isolated as a dosage-dependent suppressor of ipl1^ts mutations. DIS2SHGLC7 is predicted to encode a catalytic subunit (PP1_C) of type 1 protein phosphatase. Overexpression of the full-length DIS2SHGLC7 gene results in chromosome missegregation in wild-type cells and exacerbates the mutant phenotype in ipl1 cells. In addition, the glc7-1 mutation can partially suppress the ipl1-1 mutation. These results suggest that type 1 protein phosphatase acts in opposition to the Ipl1 protein kinase in vivo to ensure the high fidelity of chromosome segregation.