ABSTRACT
Cdc55, a regulatory B-subunit of protein phosphatase 2A (PP2A) complex, is essential for the spindle assembly checkpoint (SAC) in budding yeast, but the regulation and molecular targets of PP2A-Cdc55 have not been clearly defined or are controversial. Here, we show that an important target of Cdc55 in the SAC is the anaphase-promoting complex (APC) coupled with Cdc20 and that APC-Cdc20 is kept inactive by dephosphorylation by nuclear PP2A-Cdc55 when spindle is damaged. By isolating a new class of Cdc55 mutants specifically defective in the SAC and by artificially manipulating nucleocytoplasmic distribution of Cdc55, we further show that nuclear Cdc55 is essential for the SAC. Because the Cdc55-binding proteins Zds1 and Zds2 inhibit both nuclear accumulation of Cdc55 and SAC activity, we propose that spatial control of PP2A by Zds1 family proteins is important for tight control of SAC and mitotic progression.
Subject(s)
Anaphase-Promoting Complex-Cyclosome/metabolism , Cdc20 Proteins/metabolism , Cell Cycle Proteins/metabolism , Protein Phosphatase 2/metabolism , Saccharomyces cerevisiae Proteins/metabolism , Saccharomyces cerevisiae/metabolism , Spindle Apparatus/metabolism , Alleles , Amino Acid Sequence , Anaphase-Promoting Complex-Cyclosome/genetics , Cell Cycle Proteins/chemistry , Cell Cycle Proteins/genetics , Humans , Models, Molecular , Molecular Sequence Data , Nuclear Proteins/metabolism , Phosphorylation , Protein Phosphatase 2/chemistry , Protein Phosphatase 2/genetics , Saccharomyces cerevisiae/enzymology , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae Proteins/chemistry , Saccharomyces cerevisiae Proteins/genetics , Spindle Apparatus/enzymologyABSTRACT
We examined transition for the percentage of reticulated platelets (RP%) and platelet count in a canine case of Evans' syndrome. The result demonstrated that measurement of the RP% can be useful in evaluating platelet production in the bone marrow and response to treatment.
