The SIT4 protein phosphatase functions in late G1 for progression into S phase.
Saccharomyces cerevisiae strains containing temperature-sensitive mutations in the SIT4 protein phosphatase arrest in late G1 at the nonpermissive temperature. Order-of-function analysis shows that SIT4 is required in late G1 for progression into S phase. While the levels of SIT4 do not change in the cell cycle, SIT4 associates with two high-molecular-weight phosphoproteins in a cell-cycle-dependent fashion. In addition, we have identified a polymorphic gene, SSD1, that in some versions can suppress the lethality due to a deletion of SIT4 and can also partially suppress the phenotypic defects due to a null mutation in BCY1. The SSD1 protein is implicated in G1 control and has a region of similarity to the dis3 protein of Schizosaccharomyces pombe. We have also identified a gene, PPH2alpha, that in high copy number can partially suppress the growth defect of sit4 strains. The PPH2 alpha gene encodes a predicted protein that is 80% identical to the catalytic domain of mammalian type 2A protein phosphatases but also has an acidic amino-terminal extension not present in other phosphatases.
Sutton
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Cold Spring Harbor Laboratory, New York 11724.
Immanuel
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Arndt
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D000595:Amino Acid Sequence; D001483:Base Sequence; D003593:Cytoplasm / Q000201:enzymology; D005455:Fluorescent Antibody Technique; D016193:G1 Phase; D005796:Genes; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000235:genetics* / Q000378:metabolism; D011110:Polymorphism, Genetic; D011233:Precipitin Tests; D054648:Protein Phosphatase 2; D016196:S Phase; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins; D012689:Sequence Homology, Nucleic Acid; D013696:Temperature
D029701:Saccharomyces cerevisiae Proteins; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C104343:SIT4 protein, S cerevisiae