title: Ypi1, a positive regulator of nuclear protein phosphatase type 1 activity in Saccharomyces cerevisiae.
abstract: The catalytic subunit of protein phosphatase type 1 (PP1) has an essential role in mitosis, acting in opposition to the Ipl1/Aurora B protein kinase to ensure proper kinetochore-microtubule interactions. However, the regulatory subunit(s) that completes the PP1 holoenzyme that functions in this capacity is not known. We show here that the budding yeast Ypi1 protein is a nuclear protein that functions with PP1 (Glc7) in this mitotic role. Depletion of cellular Ypi1 induces mitotic arrest due to activation of the spindle checkpoint. Ypi1 depletion is accompanied by a reduction of nuclear PP1 and by loss of nuclear Sds22, a Glc7 binding partner that is found in a ternary complex with Ypi1 and Glc7. Expression of a Ypi1 variant that binds weakly to PP1 also activates the spindle checkpoint and suppresses the temperature sensitivity of an ipl1-2 mutant. These results, together with genetic interactions among YPI1, GLC7, and SDS22 mutants, indicate that Ypi1 and Sds22 are positive regulators of the nuclear Glc7 activity that is required for mitosis.
authors.affiliation: Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA.
authors.forename: Jennifer P
authors.initials: JP
authors.lastname: Bharucha
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Larson
authors.forename: Lu
authors.initials: L
authors.lastname: Gao
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Daves
authors.forename: Kelly
authors.initials: K
authors.lastname: Tatchell
mesh_terms: D000483:Alleles; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000201:enzymology*; D020090:Chromosome Segregation; D016195:G2 Phase; D017353:Gene Deletion; D047908:Intracellular Signaling Peptides and Proteins; D008938:Mitosis; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011485:Protein Binding; D054645:Protein Phosphatase 1 / Q000378:metabolism*; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008941:Spindle Apparatus / Q000201:enzymology; D013489:Suppression, Genetic; D013696:Temperature
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D050505:Mutant Proteins; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; C480163:Ypi1 protein, S cerevisiae; C092048:GLC7 protein, S cerevisiae; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1