THE GLC7 TYPE-1 PROTEIN PHOSPHATASE OF SACCHAROMYCES-CEREVISIAE IS REQUIRED FOR CELL-CYCLE PROGRESSION IN G(2)/M

We isolated a mutant carrying a conditional mutation in the GLC7 gene, encoding the catalytic subunit of a type 1 protein phosphatase, by selection of suppressors that restored the growth defect of cdc24 mutants at high temperature and simultaneously conferred cold-sensitive growth. This cold sensitivity for growth is caused by a single mutation (glc7(Y-170)) at position 170 of the Glc7 protein, resulting in replacement of cysteine with tyrosine. Genetic analysis suggested that the glc7(Y-170) allele is associated with a recessive negative phenotype, reducing the activity of Glc7 in the cell. The glc7(Y-170) mutant missegregated chromosome III at the permissive temperature, arrested growth as large-budded cells at the restrictive temperature, exhibited a significant increase in the number of nuclei at or in the neck, and had a short spindle. Furthermore, the glc7(Y-170) mutant exhibited a high level of CDC28-dependent protein kinase activity when incubated at the restrictive temperature. These findings suggest that the glc7(Y-170) mutation is defective in the G(2)/M phase of the cell cycle. Thus, type 1 protein phosphatase in Saccharomyces cerevisiae is essential for the G(2)/M transition.