Type 1 protein phosphatase is required for maintenance of cell wall integrity, morphogenesis and cell cycle progression in Saccharomyces cerevisiae

GLC7 encodes the catalytic subunit of type 1 protein serine/threonine phosp hatase (PP1) in the yeast Saccharomyces cerevisiae. Here we have characteri zed the temperature-sensitive glc7-10 allele, which displays aberrant bud m orphology and an abnormal actin cytoskeleton at the restrictive temperature . At 37 degrees C glc7-10 strains accumulated a high proportion of budded c ells with an unmigrated nucleus, duplicated spindle pole bodies, a short sp indle, delocalized cortical actin and 2C DNA content, indicating a cell cyc le block prior to the metaphase to anaphase transition. glc7-10 was suppres sed by growth on high osmolarity medium and exhibited temperature-sensitive cell lysis upon hypo-osmotic stress, Pkc1p, the yeast protein kinase C hom olog which is thought to regulate the Mpk1p MAP kinase pathway involved in cell wall remodelling and polarized cell growth, was found to act as a dosa ge suppressor of glc7-10. Although neither activation of BCK1 (MEKK) by the dominant BCK1-20 mutation nor increased dosage of MKK1 (MEK) or MPK1 (MAP kinase) mimicked PKC1 as a glc7-10 dosage suppressor, extra copies of genes encoding upstream components of the Pkc1p pathway such as ROM2, RHO2, HCS7 7/WSC1/SLG1 and MID2 also suppressed glc7-10 effectively. Conversely, mpk1 Delta glc7-10 and bck1 Delta glc7-10 double mutants displayed a synthetic c ell lysis defect compared with each single mutant and glc7-10 was hypersens itive to reduced PKC1 function, displaying highly aberrant morphologies and inviability even at the normally permissive temperature of 26 degrees C. D ephosphorylation by PP1 therefore functions positively to promote cell inte grity, bud morphology and polarization of the actin cytoskeleton and glc7-1 0 cells require higher levels of Pkc1p activity to sustain these functions.