title: The novel HECT-type ubiquitin-protein ligase Pub2p shares partially overlapping function with Pub1p in Schizosaccharomyces pombe.
abstract: The fission yeast Schizosaccharomyces pombe has three putative ubiquitin-protein ligases of the Nedd4/Rsp5 family, named Pub1p, Pub2p and Pub3p. Pub1p has been reported to be involved in cell cycle regulation and proliferation under acidic pH conditions. Here we characterize Pub2p, which contains a conserved HECT domain and a WW domain but lacks a C2 domain. Transcription of the pub2(+) gene was constitutive and further enhanced by nitrogen starvation. A pub2-null mutation gave no remarkable phenotypes, but intensified temperature sensitivity in a pub1Delta background. Moderately overexpressed pub2(+) suppressed the temperature sensitivity of pub1Delta cells, which suggests that the function of Pub2p overlaps with that of Pub1p. Overexpression of pub2(+) by a strong nmt1 promoter in wild-type strains caused growth arrest and cell elongation, probably owing to defects in G2 progression or the G2/M transition. Unlike Pub1p, however, overexpression of Pub2p did not reduce the levels of Cdc25p. Pub2-GFP was found throughout the cell, especially at the cell surface in the polar regions. Pub2p contains a conserved cysteine residue (Cys639) in its putative catalytic HECT domain that can be thiol-ubiquitinated. Substitution of Cys639 by alanine (Pub2CA) caused a functional defect, because growth arrest and cell elongation were not induced by overexpression of Pub2CA. A chimeric Pub1 protein, in which the HECT domain was replaced by the Pub2 HECT domain, completely suppressed the temperature sensitivity of pub1Delta cells, suggesting that the HECT domain of Pub2p has the catalytic activity of a ubiquitin ligase. We conclude that Pub2p is a HECT-type ubiquitin-protein ligase that shares partially overlapping function with Pub1p.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan.
authors.forename: Katsuyuki K
authors.initials: KK
authors.lastname: Tamai
authors.forename: Chikashi
authors.initials: C
authors.lastname: Shimoda
mesh_terms: D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D019731:Carbon-Nitrogen Ligases / Q000235:genetics* / Q000302:isolation & purification* / Q000378:metabolism*; D020134:Catalytic Domain / Q000502:physiology; D002451:Cell Compartmentation / Q000235:genetics; D056827:Endosomal Sorting Complexes Required for Transport; D019143:Evolution, Molecular; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D000075702:Nedd4 Ubiquitin Protein Ligases; D010641:Phenotype; D010802:Phylogeny; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012568:Schizosaccharomyces / Q000166:cytology / Q000201:enzymology*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics* / Q000302:isolation & purification* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases
chemical_list: D002135:Calcium-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D011993:Recombinant Fusion Proteins; D029702:Schizosaccharomyces pombe Proteins; D025801:Ubiquitin; D000075702:Nedd4 Ubiquitin Protein Ligases; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; D019731:Carbon-Nitrogen Ligases; C098922:Pub1 protein, S pombe; C467794:Pub2 protein, S pombe